Number of permutations of length n which avoid the patterns 123 and 4312.

Terms

a(0) =1a(1) =2a(2) =5a(3) =13a(4) =30a(5) =61a(6) =112a(7) =190a(8) =303a(9) =460a(10) =671a(11) =947a(12) =1300a(13) =1743a(14) =2290a(15) =2956a(16) =3757a(17) =4710a(18) =5833a(19) =7145a(20) =8666a(21) =10417a(22) =12420a(23) =14698a(24) =17275a(25) =20176a(26) =23427a(27) =27055a(28) =31088a(29) =35555