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

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =10a(5) =22a(6) =62a(7) =146a(8) =420a(9) =1050a(10) =3124a(11) =7956a(12) =23957a(13) =62486a(14) =192129a(15) =509457a(16) =1560782a(17) =4196095a(18) =13066095a(19) =35437076a(20) =109838408a(21) =301261013a(22) =944939968a(23) =2605796828a(24) =8124857765a(25) =22597326279a(26) =71095025143a(27) =198583977503