29269742059domain: NAppears in sequences2*a(n)^2 + 7 is a square.at n=27A077442a(0) = -1, a(1) = 2; a(n) = 2*a(n-1) + a(n-2).at n=28A078343Part of the y solutions of the Pell equation x^2 - 2*y^2 = +7.at n=13A253811