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Search: id:A099525
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| A099525 |
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Expansion of 1/(1-2x-3x^3). |
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+0
2
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| 1, 2, 4, 11, 28, 68, 169, 422, 1048, 2603, 6472, 16088, 39985, 99386, 247036, 614027, 1526212, 3793532, 9429145, 23436926, 58254448, 144796331, 359903440, 894570224, 2223529441, 5526769202, 13737249076, 34145086475, 84870480556
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OFFSET
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0,2
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COMMENT
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In general 1/(1-a*x-b*x^3) expands to sum{k=0..floor(n/3),C(n-2k,k)b^(n-2k)(a/b)^(n-3k)}.
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FORMULA
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a(n)=2a(n-1)+3a(n-3); a(n)=sum{k=0..floor(n/3), binomial(n-2k, k)3^(n-2k)(2/3)^(n-3k)}.
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CROSSREFS
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Sequence in context: A148131 A099412 A100094 this_sequence A024742 A024962 A122423
Adjacent sequences: A099522 A099523 A099524 this_sequence A099526 A099527 A099528
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KEYWORD
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easy,nonn
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AUTHOR
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Paul Barry (pbarry(AT)wit.ie), Oct 20 2004
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