Number of permutations of length n which avoid the patterns 312, 2341, 4321.

Terms

a(0) =1a(1) =2a(2) =5a(3) =12a(4) =25a(5) =54a(6) =120a(7) =265a(8) =580a(9) =1272a(10) =2796a(11) =6143a(12) =13488a(13) =29619a(14) =65053a(15) =142873a(16) =313771a(17) =689095a(18) =1513390a(19) =3323699a(20) =7299465a(21) =16031000a(22) =35207128a(23) =77321545a(24) =169812767a(25) =372941033a(26) =819049274a(27) =1798787604a(28) =3950478790a(29) =8676000808