A027990 Sum{T(n,k)*T(n,2n-k)}, 0<=k<=n, T given by A027926.

1, 2, 7, 21, 65, 194, 573, 1668, 4809, 13745, 39011, 110052, 308857, 862886, 2401195, 6658509, 18406373, 50738918, 139513269, 382731240, 1047768621, 2862908777, 7808872007, 21265115976, 57822787825, 157010774474, 425795804623

Offset

0,2

Links

Reinhard Zumkeller, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (5,-5,-5,5,-1).

Formula

(1/5)[n*F(2n+2) - n*F(2n-2) + 4*F(2n+1) + (-1)^n], F(n)=A000045(n). - Ralf Stephan, May 13 2004

G.f. ( 1-3*x+2*x^2+x^3 ) / ( (1+x)*(x^2-3*x+1)^2 ). - R. J. Mathar, May 22 2013

Prog

(Haskell)
a027990 n = a027990_list !! n
a027990_list = c [1] a000045_list where
   c us (v:vs) = (sum $ zipWith (*) us vs) : c (v:us) vs
-- Reinhard Zumkeller, Nov 01 2013

Crossrefs

Sequence in context: A291411 A159972 A106271 * A037520 A218836 A331722

Adjacent sequences: A027987 A027988 A027989 * A027991 A027992 A027993

Keyword

nonn

Author

Clark Kimberling

Status

approved