login
A363660
a(n) = Sum_{d|n} binomial(d+n,n).
2
2, 9, 24, 90, 258, 1043, 3440, 13419, 48850, 187836, 705444, 2725099, 10400614, 40233015, 155133856, 601820876, 2333606238, 9079958260, 35345263820, 137876637843, 538259060526, 2104292500739, 8233430727624, 32248866496625, 126410606580284
OFFSET
1,1
FORMULA
a(n) = [x^n] Sum_{k>0} (1/(1 - x^k)^(n+1) - 1).
a(n) = [x^n] Sum_{k>0} binomial(k+n,n) * x^k/(1 - x^k).
MATHEMATICA
a[n_] := DivisorSum[n, Binomial[# + n, n] &]; Array[a, 25] (* Amiram Eldar, Jul 17 2023 *)
PROG
(PARI) a(n) = sumdiv(n, d, binomial(d+n, n));
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jun 14 2023
STATUS
approved