Number of cyclic permutations of length n avoiding the pattern 321.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =4a(5) =10a(6) =24a(7) =66a(8) =178a(9) =512a(10) =1486a(11) =4446a(12) =13468a(13) =41648a(14) =130178a(15) =412670a(16) =1321418a(17) =4274970a(18) =13948966a(19) =45890440a(20) =152061154a(21) =507292698a(22) =1702753462a(23) =5748085332a(24) =19506240462