Number of homeomorphically irreducible general graphs on 3 labeled node and with n edges.

Terms

a(0) =1a(1) =3a(2) =9a(3) =21a(4) =60a(5) =135a(6) =282a(7) =537a(8) =945a(9) =1561a(10) =2451a(11) =3693a(12) =5378a(13) =7611a(14) =10512a(15) =14217a(16) =18879a(17) =24669a(18) =31777a(19) =40413a(20) =50808a(21) =63215a(22) =77910a(23) =95193a(24) =115389a(25) =138849a(26) =165951a(27) =197101a(28) =232734a(29) =273315