A362727 a(n) = [x^n] ( E(x)/E(-x) )^n where E(x) = exp( Sum_{k >= 1} A208675(k)*x^k/k ).

1, 2, 8, 110, 960, 12502, 136952, 1746558, 20951040, 267467294, 3347043208, 43051344074, 550991269824, 7146318966438, 92706899799480, 1211369977374310, 15857138035286016, 208493724775866726, 2747100161210031944, 36305149229744449050, 480750961929272288960

Offset

0,2

Comments

A208675(n) = B(n,n-1,n-1) in the notation of Straub, equation 24, where it is shown that the supercongruences A208675(n*p^k) == A208675(n*p^(k-1)) (mod p^(3*k)) hold for all primes p >= 5 and all positive integers n and k.

Links

Table of n, a(n) for n=0..20.

Armin Straub, Multivariate Apéry numbers and supercongruences of rational functions, Algebra & Number Theory, Vol. 8, No. 8 (2014), pp. 1985-2008; arXiv preprint, arXiv:1401.0854 [math.NT], 2014.

Formula

Conjecture: the supercongruence a(n*p^r) == a(n(p^(r-1)) (mod p^(3*r)) holds for

all primes p >= 7 and positive integers n and r.

Maple

A208675 := proc(n) add( (-1)^k*binomial(n-1, k)*binomial(2*n-k-1, n-k)^2, k = 0..n-1) end:
E(n, x) := series(exp(n*add(2*A208675(2*k+1)*x^(2*k+1)/(2*k+1), k = 0..10)), x, 21):
seq(coeftayl(E(n, x), x = 0, n), n = 0..20);

Crossrefs

Cf. A208675, A362722 - A362733.

Sequence in context: A374573 A132523 A012554 * A012665 A317076 A211938

Adjacent sequences: A362724 A362725 A362726 * A362728 A362729 A362730

Keyword

nonn,easy

Author

Peter Bala, May 02 2023

Status

approved