3039331domain: NAppears in sequencesa(n) = 1 - sigma(n) + sigma(n)^2 - sigma(n)^3 + sigma(n)^4.at n=19A259410a(n) = 1 - sigma(n) + sigma(n)^2 - sigma(n)^3 + sigma(n)^4.at n=25A259410