40353606domain: NAppears in sequencesa(n) = 7^n-1.at n=9A024075Jordan function J_9(n).at n=6A069094Difference of two positive 9th powers.at n=21A181128a(n) = n^9 - 1.at n=6A258810a(n) = Sum_{d|n, n/d==1 mod 4} d^9 - Sum_{d|n, n/d==3 mod 4} d^9.at n=6A321833