Number of unlabeled loopless multigraphs with n nodes of degree 3 or less.

Terms

a(0) =1a(1) =1a(2) =4a(3) =8a(4) =26a(5) =60a(6) =184a(7) =488a(8) =1509a(9) =4468a(10) =14494a(11) =47228a(12) =163584a(13) =580489a(14) =2155219a(15) =8245929a(16) =32708045a(17) =133615420a(18) =562518913a(19) =2432472970a(20) =10794454457a(21) =49060744260a(22) =228113422904