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Search: id:A123619
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| 1, 2, 13, 98, 884, 8712, 92033, 1022450, 11819620, 141052808, 1727897780, 21634496072, 275950213712, 3576314656800, 46995009879033, 625082413914450, 8403885788094500, 114069363868845000, 1561609591376307572
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OFFSET
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0,2
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COMMENT
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Related sequences: A123610(2n,n) = A123617(n); A123610(2n+1,n) = A000891(n); A123610(2n+2,n) = A123618(n).
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PROGRAM
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(PARI) {a(n)=if(n==0, 1, (1/(2*(n+1)^2))*sumdiv(2*n+2, d, if(gcd(n, d)==d, eulerphi(d)*binomial((2*n+2)/d, n/d)^2, 0)))}
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CROSSREFS
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Cf. A123610 (triangle); A123617, A000891, A123618.
Sequence in context: A118352 A074614 A064325 this_sequence A030519 A141116 A077246
Adjacent sequences: A123616 A123617 A123618 this_sequence A123620 A123621 A123622
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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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