A117353 - OEIS

A117353

Expansion of (1-x)/(1-3x+x^2+4x^3-4x^4).

1, 2, 5, 9, 18, 33, 65, 126, 253, 505, 1018, 2041, 4097, 8198, 16405, 32793, 65570, 131089, 262145, 524238, 1048493, 2097017, 4194186, 8388521, 16777281, 33554646, 67109317, 134218265, 268436018, 536871105, 1073741505, 2147482398

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OFFSET

0,2

COMMENTS

Diagonal sums of number triangle A117352.

LINKS

Table of n, a(n) for n=0..31.

Index entries for linear recurrences with constant coefficients, signature (3,-1,-4,4).

FORMULA

G.f.: (1-x)/((1-2x)(1-x-x^2+2x^3)); a(n)=3a(n-1)-a(n-2)-4a(n-3)+4a(n-4); a(n)=sum{k=0..floor(n/2), sum{j=0..n-2k, C(j-k,j)C(n-2k,j)}}.

CROSSREFS

Sequence in context: A295724 A342208 A077865 * A103422 A217210 A351983

Adjacent sequences: A117350 A117351 A117352 * A117354 A117355 A117356

KEYWORD

easy,nonn

AUTHOR

Paul Barry, Mar 09 2006

STATUS

approved