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Search: id:A116411
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| A116411 |
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Central coefficients of (1+x+x^3)^n. |
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+0
1
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| 1, 1, 1, 4, 13, 31, 76, 211, 589, 1597, 4351, 12046, 33496, 93094, 259351, 725089, 2031709, 5701189, 16023181, 45104044, 127134283, 358764613, 1013494318, 2865933907, 8111573416, 22977551656, 65138143006, 184789086106
(list; graph; listen)
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OFFSET
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0,4
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COMMENT
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Binomial transform of central coefficient of (1+x^3)^n.
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FORMULA
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a(n)=sum{k=0..floor(n/3), C(n, 3k)C(3k, k)}; a(n)=sum{k=0..n, C(n, k)*C(k, k/3)*(cos(2*pi*k/3)+1/2)*2/3}.
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CROSSREFS
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Adjacent sequences: A116408 A116409 A116410 this_sequence A116412 A116413 A116414
Sequence in context: A098536 A011937 A097122 this_sequence A106337 A027998 A026567
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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), Feb 13 2006
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