xy = x + y + 71. It implies xy - x - y + 1 = 72 (x-1)*(y-1) = 72. It has two basic solutions a) x-1 = 8, y-1 = 9, which implies x= 9, y= 10 and b) x-1 = -8, y-1 = -9, which implies x= -7, y= -8. ANSWER. There are two pairs of such integer numbers. One pair is (9,10). The other pair is (-8,-7). CHECK. 9*10 - 9 - 10 = 90 - 19 = 71. ! Correct ! (-8)*(-7) - (-8) - (-7) = 56 + 8 + 7 = 71. ! Correct !