27498621150domain: NAppears in sequencesa(n) = (2*n)!/(n!*2^(n-1)).at n=11A097801a(1) = 1, a(2) = -1, a(3) = 2; for n > 3, a(n) = -(2*n-5)*a(n-1).at n=12A129779a(1) = 1; thereafter a(n) is the product of all 0 < m < n for which a(m) divides n.at n=21A271503