A321952 Column k=7 of triangle A257673.

1, 21, 231, 1792, 11067, 58044, 268940, 1129999, 4385136, 15928948, 54711958, 179090772, 562156203, 1700628930, 4978677738, 14153099499, 39180254316, 105881154624, 279906223856, 725158329175, 1844006226090, 4608929551309, 11336379967178, 27469729015029

Offset: 7

Author

Alois P. Heinz, Nov 22 2018

Keywords

• nonn

Links

• Alois P. Heinz, Table of n, a(n) for n = 7..5000

Crossrefs

Column k=7 of A257673.

Programs

Maple

b:= proc(n, k) option remember; `if`(n=0, 1, k*add(
      b(n-j, k)*numtheory[sigma][2](j), j=1..n)/n)
    end:
a:= n-> (k-> add(b(n, k-i)*(-1)^i*binomial(k, i), i=0..k))(7):
seq(a(n), n=7..35);

Formula

G.f.: (-1 + Product_{k>=1} 1 / (1 - x^k)^k)^7. - Ilya Gutkovskiy, Jan 30 2021