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%I #21 Aug 23 2020 10:14:51
%S 1,1,3,7,13,27,54,98,174,335,572,1004,1733,2933,4916,8307,13470,22042,
%T 35851,57256,91462,145231,227667,355522,554058,853986,1313121,2010318,
%U 3057827,4627213,6989808,10481205,15679549,23365207,34658909,51241077,75541695,110852295,162238415
%N Expansion of Product_{i>=1, j>=1} (1 + i*x^(i*j)).
%H Seiichi Manyama, <a href="/A333653/b333653.txt">Table of n, a(n) for n = 0..1000</a>
%F G.f.: Product_{k>0} f(q^k) where f(q) = Product_{i>=1} (1 + i*q^i).
%F G.f.: Product_{k>0} Product_{d|k} (1 + d*x^k).
%t m = 38; CoefficientList[Series[Product[1 + i*x^(i*j), {i, 1, m}, {j, 1, m}], {x, 0, m}], x] (* _Amiram Eldar_, Aug 23 2020 *)
%o (PARI) N=40; x='x+O('x^N); Vec(prod(i=1, N, prod(j=1, N\i, 1+i*x^(i*j))))
%o (PARI) N=40; x='x+O('x^N); Vec(prod(k=1, N, prod(d=1, k, 1+(k%d==0)*d*x^k)))
%Y Cf. A022629, A107742, A285244, A318416, A332199.
%K nonn
%O 0,3
%A _Seiichi Manyama_, Aug 23 2020
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