Expansion of e.g.f.: exp(2*((1+x)^2 - 1)).

Terms

a(0) =1a(1) =4a(2) =20a(3) =112a(4) =688a(5) =4544a(6) =31936a(7) =236800a(8) =1841408a(9) =14943232a(10) =126063616a(11) =1101983744a(12) =9954734080a(13) =92714156032a(14) =888502796288