Number of combinatorial 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) =31a(11) =229a(12) =2036a(13) =21399a(14) =245342a(15) =3004881a(16) =38904499a(17) =530452205a(18) =7640941062