108833domain: NAppears in sequencesa(n) = Sum_{k=1..n} (prime(k) - 1)^n.at n=4A062440Main diagonal of Ludic array A255127 (and A255129): a(n) = A255127(n,n).at n=47A255410a(n) = Sum_{1 <= x_1, x_2, x_3 <= n} gcd(x_1, n)/gcd(x_1, x_2, x_3, n).at n=32A373060