Expansion of e.g.f. Sum_{k>=1} tanh(x^k).

Terms

a(0) =1a(1) =2a(2) =4a(3) =24a(4) =136a(5) =480a(6) =4768a(7) =40320a(8) =249856a(9) =4112640a(10) =39563008a(11) =319334400a(12) =6249389056a(13) =82473431040