A026657 a(n) = Sum_{i=0..n, j=0..n} A026648(i,j).

1, 3, 8, 18, 40, 84, 182, 378, 814, 1686, 3626, 7506, 16138, 33402, 71810, 148626, 319522, 661314, 1421714, 2942514, 6325906, 13092690, 28147058, 58255794, 125240050, 259208562, 557254322, 1153345842, 2479497394

Offset

0,2

Links

Table of n, a(n) for n=0..28.

Index entries for linear recurrences with constant coefficients, signature (1,4,-4,2,-2).

Formula

G.f.: [(1+2x)(1+x^2)]/[(1-x)(1-4x^2-2x^4)]. - Ralf Stephan, Apr 30 2004

Mathematica

LinearRecurrence[{1, 4, -4, 2, -2}, {1, 3, 8, 18, 40}, 50] (* Paolo Xausa, Feb 02 2024 *)

Prog

(PARI) a(n)=([0, 1, 0, 0, 0; 0, 0, 1, 0, 0; 0, 0, 0, 1, 0; 0, 0, 0, 0, 1; -2, 2, -4, 4, 1]^n*[1; 3; 8; 18; 40])[1, 1] \\ Charles R Greathouse IV, Jun 02 2026

Crossrefs

Cf. A026648.

Sequence in context: A369733 A026635 A135094 * A036384 A294591 A080692

Adjacent sequences: A026654 A026655 A026656 * A026658 A026659 A026660

Keyword

nonn,easy

Author

Clark Kimberling

Status

approved