Number of n X n symmetric (0,1)-matrices containing four ones.

Terms

a(0) =0a(1) =1a(2) =12a(3) =52a(4) =150a(5) =345a(6) =686a(7) =1232a(8) =2052a(9) =3225a(10) =4840a(11) =6996a(12) =9802a(13) =13377a(14) =17850a(15) =23360a(16) =30056a(17) =38097a(18) =47652a(19) =58900a(20) =72030a(21) =87241a(22) =104742a(23) =124752a(24) =147500a(25) =173225a(26) =202176a(27) =234612a(28) =270802a(29) =311025