Basis for code in A075934.

Terms

a(0) =63a(1) =455a(2) =1611a(3) =2709a(4) =12365a(5) =20630a(6) =37463a(7) =70299a(8) =135886a(9) =786510a(10) =1310867a(11) =2363919a(12) =12582995a(13) =20971674a(14) =37749317a(15) =71307271a(16) =138674310a(17) =272892511a(18) =541332108a(19) =3221225558a(20) =5368709276a(21) =9663677009a(22) =18253615171a(23) =35433742539