OFFSET
1,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..3000
FORMULA
If p is prime, a(p) = 2*p.
MATHEMATICA
a[n_] := DivisorSum[n, Binomial[n, #] * Binomial[n, n/#] &]; Array[a, 30] (* Amiram Eldar, Jun 13 2021 *)
PROG
(PARI) {a(n) = sumdiv(n, d, binomial(n, d)*binomial(n, n/d))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Mar 12 2019
STATUS
approved