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A321952 Column k=7 of triangle A257673.

%I A321952 #10 Jan 30 2021 22:50:34
%S A321952 1,21,231,1792,11067,58044,268940,1129999,4385136,15928948,54711958,
%T A321952 179090772,562156203,1700628930,4978677738,14153099499,39180254316,
%U A321952 105881154624,279906223856,725158329175,1844006226090,4608929551309,11336379967178,27469729015029
%N A321952 Column k=7 of triangle A257673.
%H A321952 Alois P. Heinz, <a href="/A321952/b321952.txt">Table of n, a(n) for n = 7..5000</a>
%F A321952 G.f.: (-1 + Product_{k>=1} 1 / (1 - x^k)^k)^7. - _Ilya Gutkovskiy_, Jan 30 2021
%p A321952 b:= proc(n, k) option remember; `if`(n=0, 1, k*add(
%p A321952       b(n-j, k)*numtheory[sigma][2](j), j=1..n)/n)
%p A321952     end:
%p A321952 a:= n-> (k-> add(b(n, k-i)*(-1)^i*binomial(k, i), i=0..k))(7):
%p A321952 seq(a(n), n=7..35);
%Y A321952 Column k=7 of A257673.
%K A321952 nonn
%O A321952 7,2
%A A321952 _Alois P. Heinz_, Nov 22 2018