Since xy2+2y divides
(2x+y)(xy2+2y)−y(2x2y+xy2+8x)=2y2−4xy,
we conclude that xy+2 divides 2y−4x. We consider two cases.
Case 1. Let 2y−4x≥0. Then we have two possibilities:
1.1) If x≥2 then xy+2>2y−4x. Hence 2y−4x=0, i.e. x=a and y=2a, where a≥2 is an integer. Since xy2+2y=4a(a2+1) divides 2x2y+xy2+8x=8a(a2+1), this gives a solution.
1.2) If x=1 then y2+2y divides 8, i.e. y=2.
Hence in this case the solutions are (a,2a), where a is a positive integer.
Case 2. Let 2y−4x<0, i.e. 4x−2y>0. If y≥4, then xy+2>4x−2. Therefore y=1,2 or 3.
2.1) If y=1 then x+22x2+9x=2x+5−x+210 is an integer. Hence x+2 divides 10 and this gives the solutions x=3,y=1 and x=8,y=1.
2.2) If y=2 then x+1x2+3x=x+2−x+12 is an integer which gives x=1.
2.3) If y=3 then 9x+66x2+17x is an integer. This implies that 3∣x, i.e. x=3k for some positive integer k. After simplifications we obtain that 9k+218k2+17k=(2k+1)+9k+24k−2 is an integer, which is impossible for k≥1.
Finally, the solutions are x=a,y=2a for all positive integers a and x=3,y=1,x=8,y=1.