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1, 4, 39, 392, 4420, 52272, 644231, 8179600, 106376580, 1410528080, 19006875580, 259613952864, 3587352778256, 50068405195200, 704925148185495, 10001318622631200, 142866058397606500, 2053248549639210000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| Related sequences: A123610(2n,n) = A123617(n); A123610(2n+1,n) = A000891(n); A123610(2n+2,n)/(n+1) = A123619(n). a(n) is divisible by (n+1): a(n)/(n+1) = A123619(n).
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PROG
| (PARI) {a(n)=if(n==0, 1, (1/(2*n+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
| Cf. A123610 (triangle); A123617, A000891, A123619.
Sequence in context: A198853 A093851 A063035 * A199757 A046449 A203211
Adjacent sequences: A123615 A123616 A123617 * A123619 A123620 A123621
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KEYWORD
| nonn
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AUTHOR
| Paul D. Hanna (pauldhanna(AT)juno.com), Oct 03 2006
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