Number of permutations of length n which avoid the patterns 123, 2431, 4132.

Terms

a(0) =1a(1) =2a(2) =5a(3) =12a(4) =24a(5) =45a(6) =83a(7) =154a(8) =290a(9) =555a(10) =1077a(11) =2112a(12) =4172a(13) =8281a(14) =16487a(15) =32886a(16) =65670a(17) =131223a(18) =262313a(19) =524476a(20) =1048784a(21) =2097381a(22) =4194555a(23) =8388882a(24) =16777514a(25) =33554755a(26) =67109213a(27) =134218104a(28) =268435860a(29) =536871345