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

Author

Clark Kimberling

Keywords

• nonn

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).

Programs

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

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