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Expansion of Product_{k>=1} (1 + (k+1)*x^k).
3

%I #9 Aug 15 2019 23:47:50

%S 1,2,3,10,13,28,58,90,146,260,481,688,1168,1748,2863,4726,6938,10412,

%T 16140,23746,35702,55812,79032,116758,168779,247006,350310,513410,

%U 744286,1045466,1485685,2098780,2935416,4137878,5746618,8027612,11343706,15487222,21418682

%N Expansion of Product_{k>=1} (1 + (k+1)*x^k).

%H Vaclav Kotesovec, <a href="/A267008/b267008.txt">Table of n, a(n) for n = 0..10000</a>

%p b:= proc(n, i) option remember; `if`(i*(i+1)/2<n, 0,

%p `if`(n=0, 1, b(n, i-1)+(1+i)*b(n-i, min(n-i, i-1))))

%p end:

%p a:= n-> b(n$2):

%p seq(a(n), n=0..42); # _Alois P. Heinz_, Aug 15 2019

%t nmax = 50; CoefficientList[Series[Product[1+(k+1)*x^k, {k, 1, nmax}], {x, 0, nmax}], x]

%t nmax = 50; poly = ConstantArray[0, nmax+1]; poly[[1]] = 1; poly[[2]] = 2; Do[Do[poly[[j+1]] += (k+1)*poly[[j-k+1]], {j, nmax, k, -1}];, {k, 2, nmax}]; poly

%Y Cf. A022629, A074141, A267007.

%K nonn

%O 0,2

%A _Vaclav Kotesovec_, Jan 08 2016