A097121 - OEIS

A097121

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

1, 1, 1, 1, 5, 17, 41, 81, 157, 337, 785, 1825, 4085, 8913, 19449, 42993, 95885, 213777, 474465, 1049921, 2323685, 5150865, 11429321, 25358737, 56233853, 124658129, 276348849, 612740961, 1358769877, 3013068113, 6681031065, 14813622577

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OFFSET

0,5

LINKS

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

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

FORMULA

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

CROSSREFS

Sequence in context: A091864 A304079 A109722 * A007904 A139545 A106972

Adjacent sequences: A097118 A097119 A097120 * A097122 A097123 A097124

KEYWORD

easy,nonn

AUTHOR

Paul Barry, Jul 25 2004

STATUS

approved