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Search: id:A108479
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| 1, 1, 2, 7, 17, 44, 117, 305, 798, 2091, 5473, 14328, 37513, 98209, 257114, 673135, 1762289, 4613732, 12078909, 31622993, 82790070, 216747219, 567451585, 1485607536, 3889371025, 10182505537, 26658145586, 69791931223, 182717648081
(list; graph; listen)
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OFFSET
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0,3
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FORMULA
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G.f.: (1-x-x^2)/(1-2x-x^2-2x^3+x^4); a(n)=2(n-1)+a(n-2)+2a(n-3)-a(n-4); a(n)=sum{k=0..floor(n/2), C(2(n-k), 2k)}; a(n)=sum{k=0..floor(n/2), sum{j=0..n-k, C(2(n-2k), j)C(2k, j)}}.
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CROSSREFS
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Sequence in context: A154117 A067038 A106910 this_sequence A014742 A085411 A007049
Adjacent sequences: A108476 A108477 A108478 this_sequence A108480 A108481 A108482
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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), Jun 04 2005
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