a(n) is the number of permutations of length n that avoid the pattern 231 and the mesh pattern (21, 204) or the same sequence for the mesh patterns (21, 206), (21, 236), (21, 238).
A289446
a(n) is the number of permutations of length n that avoid the pattern 231 and the mesh pattern (21, 204) or the same sequence for the mesh patterns (21, 206), (21, 236), (21, 238).
Terms
- a(0) =1a(1) =1a(2) =1a(3) =2a(4) =7a(5) =25a(6) =85a(7) =285a(8) =964a(9) =3310a(10) =11527a(11) =40619a(12) =144545a(13) =518680a(14) =1874713a(15) =6819033a(16) =24942773a(17) =91692355a(18) =338580112a(19) =1255267919a(20) =4670808304a(21) =17437517562a(22) =65296399663a(23) =245186344749a(24) =923016310851
External references
- oeis: A289446