197750389domain: NAppears in sequencesZsigmondy numbers for a = 7, b = 3: Zs(n, 7, 3) is the greatest divisor of 7^n - 3^n that is relatively prime to 7^m - 3^m for all positive integers m < n.at n=21A109348Expansion of 1/((1-3*x)*(1+7*x)).at n=10A201865