Number of P-graphs with 2n edges.

Terms

a(0) =1a(1) =2a(2) =7a(3) =31a(4) =167a(5) =999a(6) =6495a(7) =44619a(8) =319463a(9) =2356406a(10) =17775821a(11) =136405506a(12) =1060866006a(13) =8339982193a(14) =66147792753a(15) =528559162227