G.f.: exp( Sum_{n>=1} 2*sigma(n*3^n)*x^n/n ).

Terms

a(0) =1a(1) =8a(2) =71a(3) =478a(4) =3248a(5) =19674a(6) =116885a(7) =655064a(8) =3602627a(9) =19082622a(10) =99353815a(11) =503974610a(12) =2518347829a(13) =12341129010a(14) =59691674707a(15) =284343349874