526317901451domain: NAppears in sequencesa(n) is the number of permutations w of 1,2,...,n such that both w and w^{-1} are alternating.at n=21A007999a(n) is the number of permutations w of 1,2,...,n such that w is alternating and w^{-1} is reverse alternating.at n=21A332344