Erroneous version of A000626.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =4a(7) =11a(8) =35a(9) =101a(10) =290a(11) =804a(12) =2256a(13) =6296a(14) =17689a(15) =49952a(16) =142016a(17) =406330a(18) =1169356a(19) =3390052