A025269 a(n) = a(1)*a(n-1) + a(2)*a(n-2) + ...+ a(n-1)*a(1) for n >= 5.

2, 1, 1, 1, 6, 27, 122, 555, 2530, 11564, 52994, 243467, 1121292, 5176432, 23952042, 111076279, 516217844, 2404051080, 11218106730, 52447788512, 245659502752, 1152673780946, 5417690242696, 25505048506311, 120257626246616, 567864679387562

Offset

1,1

Links

Table of n, a(n) for n=1..26.

Formula

Conjecture: n*a(n) +4*(-2*n+3)*a(n-1) +12*(n-3)*a(n-2) +6*(2*n-9)*a(n-3) +16*(n-6)*a(n-4)=0. - R. J. Mathar, Nov 21 2014

G.f.: 1/2 - sqrt(16*x^4+12*x^3+12*x^2-8*x+1)/2. - Vaclav Kotesovec, Jan 25 2015

Mathematica

nmax = 30; aa = ConstantArray[0, nmax]; aa[[1]] = 2; aa[[2]] = 1; aa[[3]] = 1; aa[[4]] = 1; Do[aa[[n]] = Sum[aa[[k]]*aa[[n-k]], {k, 1, n-1}], {n, 5, nmax}]; aa (* Vaclav Kotesovec, Jan 25 2015 *)

Crossrefs

Sequence in context: A347781 A088152 A049270 * A265656 A137296 A329291

Adjacent sequences: A025266 A025267 A025268 * A025270 A025271 A025272

Keyword

nonn

Author

Clark Kimberling

Status

approved