A306842 a(n) = Sum_{d|n} binomial(n,d)*binomial(n,n/d).
1, 4, 6, 44, 10, 612, 14, 3936, 7074, 22700, 22, 339792, 26, 624652, 2732760, 6401232, 34, 45174204, 38, 220441080, 309304842, 325909628, 46, 7330314960, 2822796950, 6760390052, 27417926304, 78814587656, 58, 548150764560, 62, 1352747882944, 2111872688706
Offset: 1
Keywords
Links
- Seiichi Manyama, Table of n, a(n) for n = 1..3000
Programs
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Mathematica
a[n_] := DivisorSum[n, Binomial[n, #] * Binomial[n, n/#] &]; Array[a, 30] (* Amiram Eldar, Jun 13 2021 *)
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PARI
{a(n) = sumdiv(n, d, binomial(n, d)*binomial(n, n/d))}
Formula
If p is prime, a(p) = 2*p.