a(n) is the number of permutations w of 1,2,...,n such that w is alternating and w^{-1} is reverse alternating.
A332344
a(n) is the number of permutations w of 1,2,...,n such that w is alternating and w^{-1} is reverse alternating.
Terms
- a(0) =1a(1) =1a(2) =0a(3) =1a(4) =1a(5) =3a(6) =6a(7) =19a(8) =56a(9) =213a(10) =816a(11) =3717a(12) =17408a(13) =92935a(14) =513152a(15) =3147495a(16) =19993728a(17) =138638825a(18) =995169664a(19) =7700244745a(20) =61608152704a(21) =526317901451
External references
- oeis: A332344