1048976domain: NAppears in sequencesa(n) = 2^n + n^2.at n=20A001580Leyland numbers: 3, together with numbers expressible as n^k + k^n nontrivially, i.e., n,k > 1 (to avoid n = (n-1)^1 + 1^(n-1)).at n=41A076980Numbers of the form x^y + y^x, 1 < x < y.at n=35A173054