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

Terms

a(0) =1a(1) =8a(2) =52a(3) =288a(4) =1396a(5) =6208a(6) =25744a(7) =100608a(8) =374500a(9) =1336488a(10) =4596000a(11) =15297056a(12) =49444368a(13) =155640640a(14) =478268800a(15) =1437600000a(16) =4234216836a(17) =12238666208a(18) =34761065924a(19) =97130259232a(20) =267280386128a(21) =724987680384