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%I #6 Sep 26 2018 09:51:42
%S 1,1,2,4,8,15,30,58,113,220,429,835,1627,3169,6172,12023,23419,45616,
%T 88853,173073,337118,656656,1279065,2491423,4852911,9452731,18412473,
%U 35864686,69858930,136074521,265052378,516281541,1005637564,1958828336
%N Number of compositions of n with parts in N which avoid the pattern 221.
%H S. Heubach and T. Mansour, <a href="https://arxiv.org/abs/math/0603285">Enumeration of 3-letter patterns in compositions</a>, arXiv:math/0603285 [math.CO], 2006.
%F G.f.: 1/(1-Sum(x^j*Product(1-x^(2*i),i=j+1..inf),j=1..inf)).
%K nonn
%O 0,3
%A _Vladeta Jovovic_, Oct 03 2007