Number of unlabeled leafless loopless multigraphs with n edges.

Terms

a(0) =1a(1) =0a(2) =1a(3) =2a(4) =5a(5) =11a(6) =34a(7) =87a(8) =279a(9) =897a(10) =3129a(11) =11458a(12) =44576a(13) =181071a(14) =770237a(15) =3407332a(16) =15641159a(17) =74270464a(18) =364014060a(19) =1837689540a(20) =9540175803a(21) =50853577811a(22) =277976050975