242537898domain: NAppears in sequencesa(n) = (1/1 - 1/(n-1) + ... + d/binomial(n-[ n/2 ],[ n/2 ]))*L, where L = LCM{1, n-1, ..., binomial(n-[ n/2 ],[ n/2 ])}, d = (-1)^n.at n=20A025580