Number of P-graphs with 2n edges.

Terms

a(0) =1a(1) =2a(2) =7a(3) =26a(4) =114a(5) =512a(6) =2427a(7) =11794a(8) =58787a(9) =298188a(10) =1535962a(11) =8009527a(12) =42209709a(13) =224435066a(14) =1202611161a(15) =6487520874a(16) =35204691958a(17) =192042016789