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

0,3

Links

Table of n, a(n) for n=0..20.

Eric Weisstein's World of Mathematics, Permutation Pattern

Wikipedia, Permutation pattern

Example

For n = 4, the valid permutations are the 20 which are not elements of the set {1234,1324,1342,2413}, hence a(4) = 20.

Crossrefs

Cf. A033321 (avoiding 1234, 1324, 1342), A369626 (avoiding 1234, 1324, 2413), A053617 (avoiding 1234, 1324), A165530 (avoiding 1234 and 2413).

Sequence in context: A096487 A083323 A174846 * A111285 A052991 A246019

Adjacent sequences: A369428 A369429 A369430 * A369432 A369433 A369434

Keyword

nonn,more

Author

Matt Slattery-Holmes, Jan 23 2024

Extensions

a(13)-a(20) from Martin Ehrenstein, Feb 24 2024

Status

approved