Expansion of Product_{k>=1} (1 + x^k)^(4^(k-1)).

Terms

a(0) =1a(1) =1a(2) =4a(3) =20a(4) =86a(5) =390a(6) =1724a(7) =7644a(8) =33697a(9) =148401a(10) =651584a(11) =2855840a(12) =12491276a(13) =54540636a(14) =237733768a(15) =1034610232a(16) =4495832776a(17) =19508749928a(18) =84540638312a(19) =365888222552