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%I #11 Apr 05 2022 21:20:35
%S 1,1,6,39,370,4132,59288,990705,19577018,439550259,11142216938,
%T 313147651821,9680830606850,325944181383936,11875777329091878,
%U 465292113335910106,19507503314546762246,871248546067010133794,41295079536653463057146
%N Expansion of g.f. 1/(1 - Sum_{k>=1} sigma_k(k) * x^k).
%F a(0) = 1; a(n) = Sum_{k=1..n} sigma_k(k) * a(n-k).
%o (PARI) my(N=20, x='x+O('x^N)); Vec(1/(1-sum(k=1, N, sigma(k, k)*x^k)))
%o (PARI) a(n) = if(n==0, 1, sum(k=1, n, sigma(k, k)*a(n-k)));
%Y Cf. A129921, A180305, A320649.
%Y Cf. A023887, A352841, A352842.
%K nonn
%O 0,3
%A _Seiichi Manyama_, Apr 05 2022
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