A369431 a(n) is the number of permutations of [n] which avoid the patterns 1234, 1324, 1342, and 2413.
1, 1, 2, 6, 20, 66, 214, 688, 2206, 7070, 22660, 72634, 232830, 746352, 2392486, 7669286, 24584436, 78807122, 252621702, 809796400, 2595858574
Offset: 0
Examples
For n = 4, the valid permutations are the 20 which are not elements of the set {1234,1324,1342,2413}, hence a(4) = 20.
Links
- Eric Weisstein's World of Mathematics, Permutation Pattern
- Wikipedia, Permutation pattern
Crossrefs
Extensions
a(13)-a(20) from Martin Ehrenstein, Feb 24 2024