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Product_{k>=1}(1 + x^k)^a(k) = 1 + 3x.
7

%I #13 Jun 23 2018 14:17:30

%S 3,-3,8,-21,48,-116,312,-831,2184,-5880,16104,-44336,122640,-341484,

%T 956576,-2690841,7596480,-21522228,61171656,-174342144,498111952,

%U -1426403748,4093181688,-11767919276,33891544368,-97764009000

%N Product_{k>=1}(1 + x^k)^a(k) = 1 + 3x.

%H Seiichi Manyama, <a href="/A038068/b038068.txt">Table of n, a(n) for n = 1..2000</a>

%H N. J. A. Sloane, <a href="/transforms.txt">Weigh transform</a>

%F Dirichlet convolution of A038064 with characteristic function of powers of 2.

%F a(n) = 1/n*(-(-3)^n + Sum_{d<n and d|n} (-1)^(n/d)*d*a(d)). - _Seiichi Manyama_, Jun 23 2018

%Y Cf. A038063-A038070.

%K sign

%O 1,1

%A _Christian G. Bower_, Jan 04 1999