G.f. satisfies: A(x) = x*exp( Sum_{n>=1} A(sigma(n)*x^n) / n ).

Terms

a(0) =1a(1) =1a(2) =3a(3) =7a(4) =22a(5) =53a(6) =189a(7) =485a(8) =1688a(9) =4689a(10) =16650a(11) =47187a(12) =165262a(13) =485268a(14) =1728805a(15) =5174302a(16) =18049100a(17) =55269365a(18) =194672136a(19) =603386084a(20) =2099060047a(21) =6614696429a(22) =23137388920a(23) =73539215187a(24) =254877900451a(25) =819954155438