Second convolution of A107841.

Terms

a(0) =1a(1) =4a(2) =24a(3) =164a(4) =1208a(5) =9348a(6) =74920a(7) =616420a(8) =5176296a(9) =44182916a(10) =382205048a(11) =3343343268a(12) =29523386968a(13) =262826367748