A373653 - OEIS

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A373653

a(n) = Sum_{k=0..floor(n/2)} binomial(3*n-5*k-1,k).

1, 1, 1, 4, 7, 16, 34, 71, 153, 322, 686, 1455, 3088, 6558, 13917, 29548, 62721, 133146, 282646, 599998, 1273690, 2703794, 5739647, 12184181, 25864698, 54905857, 116554700, 247423522, 525233175, 1114970351, 2366870474, 5024416818, 10665883415, 22641646338

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OFFSET

0,4

LINKS

Table of n, a(n) for n=0..33.

Index entries for linear recurrences with constant coefficients, signature (1,3,0,-3,0,1).

FORMULA

G.f.: 1 / (1 - x/(1 - x^2)^3).

a(n) = a(n-1) + 3*a(n-2) - 3*a(n-4) + a(n-6) for n > 6.

PROG

(PARI) a(n) = sum(k=0, n\2, binomial(3*n-5*k-1, k));

CROSSREFS