a(n) is the number of permutations of [n] which avoid the patterns 1234, 1324, 1342, and 2413.

A369431

a(n) is the number of permutations of [n] which avoid the patterns 1234, 1324, 1342, and 2413.

Terms

    a(0) =1a(1) =1a(2) =2a(3) =6a(4) =20a(5) =66a(6) =214a(7) =688a(8) =2206a(9) =7070a(10) =22660a(11) =72634a(12) =232830a(13) =746352a(14) =2392486a(15) =7669286a(16) =24584436a(17) =78807122a(18) =252621702a(19) =809796400a(20) =2595858574

External references