O.g.f.: exp( Sum_{n>=1} (sigma(2*n)-sigma(n))^2/2 * x^n/n ).

Terms

a(0) =1a(1) =2a(2) =6a(3) =20a(4) =46a(5) =116a(6) =284a(7) =632a(8) =1414a(9) =3102a(10) =6536a(11) =13636a(12) =28020a(13) =56300a(14) =111888a(15) =219608a(16) =424694a(17) =813104a(18) =1540818a(19) =2888060a(20) =5366072a(21) =9884616a(22) =18050428a(23) =32713048a(24) =58851972a(25) =105113942a(26) =186505864a(27) =328821408a(28) =576153008a(29) =1003687444