A369431 - OEIS

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

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OFFSET

0,3

LINKS

Eric Weisstein's World of Mathematics, 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).

KEYWORD

nonn,more

AUTHOR

EXTENSIONS

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

STATUS

approved