OFFSET
0,6
LINKS
Ray Chandler, Table of n, a(n) for n = 0..3340 (terms < 10^1000; first 101 terms from T. D. Noe)
FORMULA
a(n) equals the coefficient of x in Product_{k=1..n} (x^k + 1/x^k). - Paul D. Hanna, Jul 10 2018
MATHEMATICA
f[n_, s_] := f[n, s]=Which[n==0, If[s==0, 1, 0], Abs[s]>(n*(n+1))/2, 0, True, f[ n-1, s-n]+f[n-1, s+n]]; a[n_] := f[n, 1]
nmax = 50; d = {1}; a1 = {};
Do[
i = Ceiling[Length[d]/2] + 1;
AppendTo[a1, If[i > Length[d], 0, d[[i]]]];
d = PadLeft[d, Length[d] + 2 n] + PadRight[d, Length[d] + 2 n];
, {n, nmax}];
a1 (* Ray Chandler, Mar 14 2014 *)
CROSSREFS
KEYWORD
nonn,easy,nice
AUTHOR
N. J. A. Sloane, following a suggestion by J. H. Conway, Aug 27 2001
EXTENSIONS
More terms from Dean Hickerson and Vladeta Jovovic, Aug 28 2001
STATUS
approved