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Search: id:A097122
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A097122 Expansion of (1-x)^2/((1-x)^3-3x^3). +0
2
1, 1, 1, 4, 13, 31, 70, 169, 421, 1036, 2521, 6139, 14998, 36661, 89545, 218644, 533941, 1304071, 3184966, 7778449, 18996733, 46394716, 113307745, 276726019, 675833686, 1650553981, 4031064961, 9844867684, 24043624093, 58720529071 (list; graph; listen)
OFFSET

0,4

FORMULA

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

CROSSREFS

Cf. A024493, A052101.

Sequence in context: A097120 A098536 A011937 this_sequence A116411 A106337 A027998

Adjacent sequences: A097119 A097120 A097121 this_sequence A097123 A097124 A097125

KEYWORD

easy,nonn

AUTHOR

Paul Barry (pbarry(AT)wit.ie), Jul 25 2004

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Last modified July 25 07:41 EDT 2008. Contains 142293 sequences.


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