O.g.f.: exp( Sum_{n>=1} (sigma(2*n^4) - sigma(n^4)) * x^n/n ).

Terms

a(0) =1a(1) =2a(2) =18a(3) =114a(4) =450a(5) =2298a(6) =10466a(7) =43314a(8) =184402a(9) =749490a(10) =2942274a(11) =11437026a(12) =43364818a(13) =161089130a(14) =589901682a(15) =2123791130a(16) =7531395154a(17) =26360805018a(18) =91057065522a(19) =310718196626