E.g.f.: Product_{k>=1} 1/(1 - x^(4*k-1)/(4*k-1)).

Terms

a(0) =1a(1) =0a(2) =0a(3) =2a(4) =0a(5) =0a(6) =80a(7) =720a(8) =0a(9) =13440a(10) =172800a(11) =3628800a(12) =5913600a(13) =98841600a(14) =4420915200a(15) =92559667200a(16) =110702592000