Closed walks of length n in K_4 graph.

Terms

a(0) =0a(1) =12a(2) =24a(3) =84a(4) =240a(5) =732a(6) =2184a(7) =6564a(8) =19680a(9) =59052a(10) =177144a(11) =531444a(12) =1594320a(13) =4782972a(14) =14348904a(15) =43046724a(16) =129140160a(17) =387420492a(18) =1162261464a(19) =3486784404a(20) =10460353200a(21) =31381059612a(22) =94143178824a(23) =282429536484a(24) =847288609440