E.g.f.: exp(x^3/(1 + x + x^2 + x^3)).

Terms

a(0) =1a(1) =0a(2) =0a(3) =6a(4) =-24a(5) =0a(6) =360a(7) =0a(8) =-20160a(9) =60480a(10) =1814400a(11) =-19958400a(12) =-59875200a(13) =2075673600a(14) =21794572800a(15) =-860885625600