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Search: id:A098477
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| A098477 |
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Expansion of 1/sqrt(1-2x-7x^2+8x^3). |
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+0
2
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| 1, 1, 5, 9, 37, 89, 325, 905, 3109, 9337, 31173, 97449, 321445, 1027225, 3374405, 10920649, 35855909, 116937145, 384340421, 1259728873, 4147000229, 13639616473, 44978045765, 148314302473, 489879442469, 1618600915705
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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1/sqrt(1-2x-(4r-1)x^2+4r^3) expands to give sum{k=0..floor(n/2), binomial(2k,k)binomial(n-k,n-2k)r^k}
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FORMULA
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a(n)=sum{k=0..floor(n/2), binomial(2k, k)binomial(n-k, n-2k)2^k}
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CROSSREFS
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Cf. A026569, A098478.
Sequence in context: A098640 A083832 A070969 this_sequence A110421 A123822 A121724
Adjacent sequences: A098474 A098475 A098476 this_sequence A098478 A098479 A098480
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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), Sep 10 2004
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