Number of multigraphs on 4 unlabeled nodes with n edges where the edges can be of two colors.

Terms

a(0) =1a(1) =2a(2) =9a(3) =30a(4) =90a(5) =248a(6) =650a(7) =1560a(8) =3560a(9) =7680a(10) =15786a(11) =31076a(12) =58905a(13) =107768a(14) =191180a(15) =329664a(16) =554038a(17) =909558a(18) =1461655a(19) =2302950a(20) =3563482a(21) =5422392a(22) =8124040a(23) =11997648a(24) =17482295a(25) =25156872a(26) =35779092a(27) =50330364a(28) =70072640a(29) =96615760