Expansion of g.f.: exp( Sum_{n>=1} 2^n*(Sum_{d|n} d*x^d)^n/n ).

Terms

a(0) =1a(1) =2a(2) =4a(3) =16a(4) =40a(5) =136a(6) =400a(7) =1256a(8) =4272a(9) =14984a(10) =51856a(11) =174304a(12) =563776a(13) =1820672a(14) =5780864a(15) =18518912a(16) =61112832a(17) =213235904a(18) =775157504a(19) =2859529984a(20) =10441532416a(21) =37338042528a(22) =130397329216a(23) =447932053120