Vela Mathematics Program: problems

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63 problems · 1/2Number SourcesGraph view

declared open · formalizederdos:11

∀ (n : ℕ), Odd n → 1 < n → ∃ k l, Squarefree k ∧ n = k + 2 ^ l

number theoryadditive basisA001220 · A3775873 sources

declared open · formalizederdos:12

A \subset \mathbb{N}

be infinite with no distinct

a, b, c \in A

such that

a \mid (b + c)

with

b, c > a

. Can

|A \cap [1, N]|/\sqrt{N}

have positive lower limit? Must every such

A

fall below

N^{1-c}

infinitely often?

number theoryN/A4 sources

declared open · formalizederdos:25

True ↔ ∀ (seq_n : ℕ → ℕ) (seq_a : ℕ → ℤ), (∀ (i : ℕ), 0 < seq_n i) → StrictMono seq_n → ∃ d, {x | ∀ (i : ℕ), ↑x < ↑(seq_n i) ∨ ¬↑x ≡ seq_a i [ZMOD ↑(seq_n i)]}.HasLogDensity d

number theoryN/A3 sources

declared open · formalizederdos:36

Erdos36.M 5 = 3

number theoryadditive combinatoricsA393584 · possible3 sources

declared open · formalizederdos:51

True ↔ ∃ A n, A.Infinite ∧ (∀ (a : ↑A), IsLeast (Nat.totient ⁻¹' {↑a}) (n a)) ∧ Filter.Tendsto (fun a => ↑(n a) / ↑↑a) Filter.atTop Filter.atTop

number theoryA002202 · A0141973 sources

declared open · formalized · $250erdos:52

True ↔ ∀ (ε : ℝ), 0 < ε → ε < 1 → ∃ C, 0 < C ∧ ∀ (A : Finset ℤ), max ↑(A + A).card ↑(A * A).card ≥ C * ↑A.card ^ (2 - ε)

number theoryadditive combinatoricsA2639963 sources

declared open · formalizederdos:75

True ↔ ∃ V G, G.chromaticCardinal = Cardinal.aleph 1 ∧ Cardinal.mk V = Cardinal.aleph 1 ∧ ∀ ε > 0, ∀ᶠ (n : ℕ) in Filter.atTop, ∀ (H : G.Subgraph), H.verts.ncard = n → ∃ I, ↑I ⊆ H.verts ∧ G.IsIndepSet ↑I ∧ ↑I.card > ↑n ^ (1 - ε)

graph theorychromatic numberN/A3 sources

declared open · formalized · $100erdos:120

True ↔ ∀ (A : Set ℝ), A.Infinite → Erdos120.Erdos120For A

combinatoricsN/A3 sources

declared open · formalizederdos:124

∀ {D : Finset ℕ}, (∀ d ∈ D, 3 ≤ d) → (∀ᶠ (n : ℕ) in Filter.atTop, n ∈ ∑ d ∈ D, Erdos124.sumsOfDistinctPowers d 0) → 1 ≤ ∑ d ∈ D, (↑d - 1)⁻¹

number theorybase representationsN/A4 sources

declared open · formalized · $500erdos:138

W(k)

is the least

N

such that every two-colouring of

\{1, \dots, N\}

contains a monochromatic

k

-term arithmetic progression, must

W(k+1) - W(k) \to \infty

additive combinatoricsA0053464 sources

declared open · formalizederdos:218

{n | primeGap (n + 1) ≤ primeGap n}.HasDensity (1 / 2)

number theoryprimesA333230 · A333231 · A0641133 sources

declared open · formalizederdos:233

(fun N => ∑ n ∈ Finset.range N, ↑(primeGap n) ^ 2) =O[Filter.atTop] fun N => ↑N * Real.log ↑N ^ 2

number theoryprimesA0747413 sources

declared open · formalizederdos:251

True ↔ Irrational (∑' (n : ℕ), ↑(Nat.nth Nat.Prime n) / 2 ^ n)

number theoryirrationalityA0989903 sources

declared open · formalizederdos:263

sorry ↔ Erdos263.IsIrrationalitySequence fun n => 2 ^ 2 ^ n

irrationalityN/A3 sources

declared open · formalizederdos:264

¬Erdos264.IsIrrationalitySequence fun x => 2 ^ x

irrationalityN/A4 sources

declared open · formalizederdos:288

sorry ↔ {I | ∀ (j : Fin 2), (I j).1 ≤ (I j).2 ∧ ∃ n, ∑ j, ∑ nⱼ ∈ (Set.Icc (I j).1 (I j).2).toFinset, (↑↑nⱼ)⁻¹ = ↑↑n}.Finite

number theoryunit fractionsN/A3 sources

declared open · formalizederdos:306

a/b \in \mathbb{Q}_{>0}

and

b

is squarefree, can

a/b

always be written as a finite sum of reciprocals of distinct products of two distinct primes?

number theoryunit fractionsN/A4 sources

declared open · formalizederdos:326

Does there exist

A=\{a_1<a_2<\cdots\}\subset \mathbb{N}

which is a minimal basis of order

2

(every large integer is the sum of

2

elements from

A

, and no proper subset of

A

has this property) such that

\lim_{k\to \infty}a_k/k^2=c

for some

c\neq 0

? A claimed construction gives a minimal basis with

A(x)=C\sqrt{x}+O(1)

, answering the question affirmatively; Erdős and Graham had conjectured a negative answer.

number theoryadditive basisN/A4 sources

declared open · formalizederdos:342

sorry ↔ ∀ (a : ℕ → ℕ), Erdos342.IsUlamSequence a → {n | ∃ m, a m = a n + 2}.Infinite

number theoryA0028583 sources

declared open · formalizederdos:346

Let

A=\{1\leq a_1< a_2<\cdots\}

be a set of integers such that

A\backslash B

is complete for any finite subset

B

and not complete for any infinite subset

B

. If

a_{n+1}/a_n \geq 1+\epsilon

for all

n

, must

\lim_n a_{n+1}/a_n=(1+\sqrt{5})/2

? Under the reading where the ratio limit is assumed to exist, a Lean-verified argument forces the limit to be the golden ratio; a separate construction disproves the literal statement where convergence is not assumed.

number theorycomplete sequencesN/A4 sources

declared open · formalizederdos:349

∀ (t α : ℝ), 0 < t → 2 < α → ¬Erdos349.IsGoodPair t α

number theorycomplete sequencesN/A3 sources

declared open · formalizederdos:352

True ↔ ∃ c > 0, ∀ (A : Set (EuclideanSpace ℝ (Fin 2))), MeasurableSet A → ↑(MeasureTheory.volume A) ≥ ↑c → ∃ t, (∀ (p : Fin 3), t.points p ∈ A) ∧ EuclideanGeometry.triangle_area (t.points 0) (t.points 1) (t.points 2) = 1

geometryN/A3 sources

declared open · formalizederdos:390

Let

f(n)

be the least

m

for which

n!

can be written as

a_1\cdots a_k

with

n < a_1 < \cdots < a_k = m

- the smallest possible largest factor in a factorization of

n!

into distinct integers all exceeding

n

. Erdős, Guy and Selfridge proved

f(n) - 2n \asymp n/\log n

. Erdős asked whether there is a constant

c

with

f(n) - 2n \sim c\,\frac{n}{\log n},

and what it is. This preprint answers yes and names the constant:

\lim_{n\to\infty}\frac{(f(n)-2n)\log n}{n} = \frac{4029639598}{25970038185} \approx 0.15516.

number theoryfactorialsA1934294 sources

declared open · formalizederdos:396

True ↔ ∀ (k : ℕ), ∃ n, n.descFactorial (k + 1) ∣ n.centralBinom

number theorybinomial coefficientsA3750773 sources

declared open · formalizederdos:400

True ↔ ∀ k ≥ 2, ∃ c, Asymptotics.IsEquivalent Filter.atTop (fun x => ∑ n ∈ Finset.Icc 1 x, ↑(Erdos400.g k n)) fun x => c * ↑x * Real.log ↑x

number theoryfactorialspossible3 sources

declared open · formalizederdos:456

True ↔ Filter.Tendsto (fun N => ↑(Nat.count {n | Erdos456.m n < Erdos456.p n} N) / ↑N) Filter.atTop (nhds 1)

number theoryA034694 · A061026 · possible3 sources

declared open · formalizederdos:477

Does there exist an integer polynomial

f

of degree at least two and a set

A \subseteq \mathbb{Z}

such that every integer has a unique representation

n = a + f(k)

? A manuscript claims the thirteenth powers admit a tiling complement.

number theoryN/A4 sources

declared open · formalizederdos:501

For every

x \in \mathbb{R}

let

A_x \subset \mathbb{R}

be a bounded set of Lebesgue outer measure

< 1

. Must there be an infinite independent set, that is an infinite

X \subseteq \mathbb{R}

with

x \notin A_y

for all distinct

x, y \in X

? Erdős and Hajnal proved that arbitrarily large finite independent sets exist. Hechler showed in 1972 that the answer is no under the continuum hypothesis, so any positive answer had to come from a model where CH fails, and Sungchul Lee later derived one from a real-valued measurable cardinal. The answer is that neither side is provable. Dropping Lee's large cardinal by transferring his argument to the extension of a model of CH by random reals gives a model where the answer is yes; Hechler's construction gives one where it is no. The question is independent of ZFC.

combinatoricsset theoryN/A4 sources

declared open · formalizederdos:503

∀ (n : ℕ), IsGreatest {x | ∃ A, ∃ (_ : A.IsIsosceles), A.ncard = x} sorry

geometrydistancesA1757693 sources

declared open · formalizederdos:507

Asymptotics.IsEquivalent Filter.atTop Erdos507.α sorry

geometryN/A3 sources

declared open · formalizederdos:513

sorry = ⨆ f, Filter.liminf (fun r => Erdos513.ratio r ↑f) Filter.atTop

analysisN/A3 sources

declared open · formalizederdos:521

False ↔ Erdos521.Claim

analysispolynomialsprobabilityN/A4 sources

declared open · formalizederdos:535

∀ r ≥ 3, ∃ c > 0, ∀ᶠ (N : ℕ) in Filter.atTop, ↑(Erdos535.f r N) ≤ ↑N ^ (c / Real.log (Real.log ↑N))

number theorypossible3 sources

declared open · formalizederdos:536

True ↔ ∀ ε > 0, ∀ᶠ (N : ℕ) in Filter.atTop, ∀ A ⊆ Finset.Icc 1 N, ε * ↑N ≤ ↑A.card → ∃ a ∈ A, ∃ b ∈ A, ∃ c ∈ A, {a, b, c}.card = 3 ∧ a.lcm b = b.lcm c ∧ b.lcm c = a.lcm c

number theorypossible3 sources

declared open · formalizederdos:539

For

|A| = n

, how small can the cofactor set

Q(A) = \{a / \gcd(a,b) : a, b \in A\}

be? The answer is

h(n) = n^{1/2 + o(1)}

: a new upper bound

h(n) \le n^{1/2} \exp(O(\sqrt{\log n}))

matches the classical lower bound.

number theorypossible5 sources

declared open · formalized · $500erdos:593

Which finite triple systems occur in every triple system of uncountable chromatic number? The claimed characterization: exactly those that, after removing isolated vertices, are linear, have every hyperedge-node of their Levi graph meeting a bridge, and have every Berge cycle even.

set theorygraph theoryhypergraphsN/A4 sources

declared open · formalizederdos:598

∀ (m : Type u_1) [Infinite m], True ↔ ∃ c, ∀ (X : Set m), Cardinal.mk ↑X = Erdos598.κ → c '' {s | ↑s ⊆ X} = Set.univ

set theoryramsey theoryN/A3 sources

declared open · formalizederdos:623

Let

X

be a set of cardinality

\aleph_\omega

and

f

a function from the finite subsets of

X

X

such that

f(A)\not\in A

for all

A

. Must there exist an infinite independent

Y\subseteq X

, i.e. with

f(B)\not\in Y

for all finite

B\subset Y

? Claimed resolution: the positive assertion is equivalent to Koepke's free-subset property, hence independent of ZFC, with consistency strength exactly a measurable cardinal.

set theoryN/A4 sources

declared open · formalizederdos:686

sorry ↔ ∀ N ≥ 2, ∃ k ≥ 2, ∃ n, ∃ m ≥ n + k, ↑N = ↑(∏ i ∈ Finset.Icc 1 k, (m + i)) / ↑(∏ i ∈ Finset.Icc 1 k, (n + i))

number theoryN/A4 sources

declared open · formalizederdos:689

sorry ↔ ∀ᶠ (n : ℕ) in Filter.atTop, ∃ a, ∀ m ∈ Finset.Icc 1 n, 2 ≤ {p ∈ Finset.Icc 1 n | Nat.Prime p ∧ a p ≡ m [MOD p]}.card

number theoryN/A3 sources

declared open · formalizederdos:730

True ↔ Erdos730.S.Infinite

number theorybinomial coefficientsbase representationsA1295154 sources

declared open · formalizederdos:749

True ↔ ∀ ε > 0, ∃ A, 1 - ε ≤ (A + A).lowerDensity ∧ (Nat.cast ∘ AdditiveCombinatorics.sumRep A) =O[Filter.atTop] fun n => 1

additive combinatoricsN/A3 sources

declared open · formalizederdos:872

True ↔ ∃ ε > 0, ∀ᶠ (n : ℕ) in Filter.atTop, ↑(Erdos872.L n) ≥ ε * ↑n

number theoryprimitive setspossible3 sources

declared open · formalizederdos:873

True ↔ ∀ (a : ℕ → ℕ), ∀ ε > 0, 0 < a 0 → StrictMono a → ∃ k, ∀ X > 0, ↑↑(Erdos873.F a X k) < ↑(X ^ ε)

number theoryN/A3 sources

declared open · formalizederdos:906

Is there an entire non-zero function

f:\mathbb{C}\to \mathbb{C}

such that, for any infinite sequence

n_1<n_2<\cdots

, the set

\{ z: f^{(n_k)}(z)=0 \textrm{ for some }k\geq 1\}

is everywhere dense? The literal question is trivial for polynomials, so the claims address the transcendental entire case, in the affirmative.

analysisiterated functionsN/A5 sources

declared open · formalizederdos:931

sorry ↔ ∀ (k₁ k₂ : ℕ), k₂ ≥ 3 → k₂ ≤ k₁ → {(n₁, n₂) | n₁ + k₁ ≤ n₂ ∧ (∏ i ∈ Finset.Icc 1 k₁, (n₁ + i)).primeFactors = (∏ j ∈ Finset.Icc 1 k₂, (n₂ + j)).primeFactors}.Finite

number theoryN/A3 sources

declared open · formalizederdos:942

Let

h(n)

count powerful integers in

[n^2, (n+1)^2)

. What is the extremal order of

h(n)

number theorypossible4 sources

declared open · formalizederdos:943

True ↔ ∃ o, o =o[Filter.atTop] 1 ∧ ∀ᶠ (n : ℕ) in Filter.atTop, ↑(AdditiveCombinatorics.sumRep Nat.Powerful n) ≤ ↑n ^ o n

number theorypossible4 sources

declared open · formalizederdos:949

True ↔ ∀ (S : Set ℝ), (∀ a ∈ S, ∀ b ∈ S, a + b ∉ S) → ∃ A ⊆ Sᶜ, Cardinal.mk ↑A = Cardinal.continuum ∧ A + A ⊆ Sᶜ

ramsey theoryN/A3 sources

declared open · formalizederdos:951

sorry ↔ ∀ (a : ℕ → ℝ), 1 < a 0 → StrictMono a → Erdos951.Erdos951Prop a → ∀ᶠ (x : ℝ) in Filter.atTop, {i | a i ≤ x}.ncard ≤ ⌊x⌋₊.primeCounting

number theoryN/A3 sources

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