Number of self-polar configurations of type (n_3).

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =1a(7) =1a(8) =3a(9) =10a(10) =25a(11) =95a(12) =365a(13) =1432a(14) =5799a(15) =24092a(16) =102413a(17) =445363a(18) =1991320