14213945668domain: NAppears in sequencesPositive integers making n^2*(n-1)*(2*n-1)^2*(7*n-1)/36 a square.at n=9A073352a(0) = a(1) = a(2) = 1; for n > 2, a(n) = (a(n-1) + 1)*(a(n-2) + 1) / a(n-3).at n=19A276123