Row 2 of table A111528.

Terms

a(0) =1a(1) =1a(2) =4a(3) =22a(4) =148a(5) =1156a(6) =10192a(7) =99688a(8) =1069168a(9) =12468208a(10) =157071424a(11) =2126386912a(12) =30797423680a(13) =475378906432