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A027990 Sum{T(n,k)*T(n,2n-k)}, 0<=k<=n, T given by A027926. 1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified February 24 08:41 EST 2020. Contains 332203 sequences. (Running on oeis4.)