833994048910domain: NAppears in sequencesa(n) = n^9 + n^8 + n^7 + n^6 + n^5 + n^4 + n^3 + n^2 + n + 1.at n=21A103623a(n) = (21^n - 1)/20.at n=10A218724a(n) = ((2*n + 1)^n - 1)/(2*n).at n=9A361291