As always in such problems, let me start with the Answer. The numbers are (-5,-3) or (7,9). Check. (-5)*(-3) = 15; 2*((-5)+ (-3) = 2*(-8) = - 16, and 15 = -16 + 31. ! Correct ! 7*9 = 63; 2*(7+9) = 2*16 = 32, and 63 = 32 + 31. ! Correct !
Let n be the integer number exactly half-way between two consecutive odd integers. Then the conditions says: n^2 -1 = 4n + 31 ====> n^2 - 4n - 32 = 0 ====> (n+4)*(n-8) = 0 ====> there are TWO solutions for n: n= -4 and n= 8, what give you the answer.