Main diagonal of triangle A100235.

Terms

a(0) =1a(1) =4a(2) =26a(3) =139a(4) =726a(5) =3774a(6) =19601a(7) =101784a(8) =528526a(9) =2744419a(10) =14250626a(11) =73997554a(12) =384238401a(13) =1995189564a(14) =10360186226a(15) =53796120699a(16) =279340789726