G.f.: A(x) = exp( Sum_{n>=1} sigma(n)^2*x^n/n ), a power series in x with integer coefficients.

Terms

a(0) =1a(1) =1a(2) =5a(3) =10a(4) =30a(5) =57a(6) =152a(7) =289a(8) =676a(9) =1304a(10) =2809a(11) =5335a(12) =10961a(13) =20487a(14) =40329a(15) =74476a(16) =141914a(17) =258094a(18) =479638a(19) =860025a(20) =1563716a(21) =2767982a(22) =4940567a(23) =8636563a(24) =15173805a(25) =26217392a(26) =45416811a(27) =77629455a(28) =132800937a(29) =224695510