85824domain: NAppears in sequencesa(n) = Sum_{k=1..n} floor(k/2)! * floor((n - k)/2)! binomial((n-floor(k/2)-1), n-k).at n=13A339150a(n) is the least number k such that the equation phi(x) = k has exactly n solutions and the arithmetic mean of these solutions is an integer, or -1 if no such number exists.at n=36A389860