A diagonal of triangle A187115.

Terms

a(0) =1a(1) =4a(2) =20a(3) =138a(4) =1258a(5) =14476a(6) =202655a(7) =3354848a(8) =64246776a(9) =1398909332a(10) =34157026526a(11) =924757926320