Number of permutations of [n] having exactly three adjacent 4-cycles.

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) =1a(13) =4a(14) =20a(15) =120a(16) =836a(17) =6700a(18) =60360a(19) =603960a(20) =6646090a(21) =79773180a(22) =1037232420a(23) =14523065760a(24) =217865924620