Number of disconnected 4-regular simple graphs on n vertices with girth exactly 4.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =0a(8) =0a(9) =0a(10) =0a(11) =0a(12) =0a(13) =0a(14) =0a(15) =0a(16) =1a(17) =0a(18) =2a(19) =2a(20) =15a(21) =35a(22) =247a(23) =1692a(24) =17409a(25) =197924a(26) =2492824a(27) =33117880a(28) =461597957a(29) =6709514218