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Search: id:A123612
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| 1, 1, 2, 3, 5, 8, 17, 31, 68, 145, 325, 728, 1685, 3891, 9140, 21565, 51311, 122666, 295037, 712477, 1728262, 4207027, 10276693, 25178708, 61866141, 152397945, 376309596, 931239093, 2309219447, 5737078442, 14278587533, 35595622719
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OFFSET
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0,3
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PROGRAM
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(PARI) {a(n)=sum(k=0, n\2, if(k==0, 1, (1/(n-k))*sumdiv(n-k, d, if(gcd(k, d)==d, eulerphi(d)*binomial((n-k)/d, k/d)^2, 0))))}
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CROSSREFS
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Cf. A123610 (triangle), A123611 (row sums); central terms: A123617, A123618.
Sequence in context: A093000 A122630 A108054 this_sequence A077177 A145793 A113879
Adjacent sequences: A123609 A123610 A123611 this_sequence A123613 A123614 A123615
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KEYWORD
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nonn
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AUTHOR
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Paul D. Hanna (pauldhanna(AT)juno.com), Oct 03 2006
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