57290domain: NAppears in sequencesCoefficient of x in the reduction by x^2->x+1 of the polynomial p(n,x) defined below in Comments.at n=20A192760Coefficients of the generalized continued fraction expansion sqrt(7) = a(1) +a(1)/(a(2) +a(2)/(a(3) +a(3)/(a(4) +a(4)/....))).at n=13A233587