Arises in enumerating non-degenerate colorings in Brook's Theorem.

Terms

a(0) =6a(1) =68a(2) =252a(3) =648a(4) =1370a(5) =2556a(6) =4368a(7) =6992a(8) =10638a(9) =15540a(10) =21956a(11) =30168a(12) =40482a(13) =53228a(14) =68760a(15) =87456a(16) =109718a(17) =135972a(18) =166668a(19) =202280a(20) =243306a(21) =290268a(22) =343712a(23) =404208a(24) =472350a(25) =548756a(26) =634068a(27) =728952a(28) =834098a(29) =950220