Number of cyclic permutations of length n avoiding the pattern 123.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =4a(5) =10a(6) =24a(7) =68a(8) =188a(9) =586a(10) =1722a(11) =5492a(12) =16924a(13) =55582a(14) =177278a(15) =594460a(16) =1944980a(17) =6628384a(18) =22132112a(19) =76421498a(20) =259359036a(21) =905416294a(22) =3114033930a(23) =10971347070a(24) =38157201530