A357959 a(n) = 5*A005259(n-1) + 2*A005258(n).

11, 63, 659, 9727, 187511, 4304943, 109312739, 2941124607, 82033399631, 2345394917563, 68306797052879, 2018580243252847, 60368874298729631, 1823588997226603663, 55558079041172790659, 1705174802761490321407, 52672634815976274443711, 1636296942340074307669443

Offset

1,1

Comments

Conjectures:

1) a(p) == a(1) (mod p^5) for all primes p >= 5 (checked up to p = 271).

2) a(p^r) == a(p^(r-1)) ( mod p^(3*r+3) ) for r >= 2, and for all primes p >= 5.

These are stronger supercongruences than those satisfied separately by the two types of Apéry numbers A005258 and A005259. Cf. A357959.

There is also a product version of these conjectures:

3) the sequence {u(n): n >= 1} defined by u(n) = A005259(n-1)^5 * A005258(n)^6 also satisfies the congruences in 1) and 2) above. See A357960.

Links

Table of n, a(n) for n=1..18.

Formula

a(n) = 5*Sum_{k = 0..n-1} binomial(n-1,k)^2*binomial(n+k-1,k)^2 + 2*Sum_{k = 0..n} binomial(n,k)^2*binomial(n+k,k).

a(n*p^r) == a(n*p^(r-1)) ( mod p^(3*r) ) for positive integers n and r and for all primes p >= 5.

Example

Examples of supercongruences:
a(13) - a(1) = 60368874298729631 - 11 = (2^2)*3*5*(13^5)*131*20685869 == 0 (mod 13^5).
a(5^2) - a(5) = 51292638914356604042099497031437511 - 187511 = (2^4)*3*(5^10)* 37*72974432287*40526706713533 == 0 (mod 5^10).

Maple

seq( add( 5*binomial(n-1, k)^2*binomial(n+k-1, k)^2 + 2*binomial(n, k)^2* binomial(n+k, k), k = 0..n ), n = 1..20);

Crossrefs

Cf. A005258, A005259, A212334, A352655, A357567, A357956, A356957, A357958, A357960.

Sequence in context: A163706 A180763 A362164 * A285361 A237358 A250604

Adjacent sequences: A357956 A357957 A357958 * A357960 A357961 A357962

Keyword

nonn,easy

Author

Peter Bala, Oct 25 2022

Status

approved