Răspuns :
Divizorii lui 20:{1,2,4,5,10,20}
2n+2=1=>2n=-1=>n=-1/2
2n+2=2=>2n=0=>n=0
2n+2=4=>2n=2=>n=1
2n+2=5=>2n=3=>n=3/2
2n+2=10=>2n=8=>n=4
2n+2=20=>2n=18=>n=9
Dar n este numar natural => n∈{0,1,4,9}
2n+2=1=>2n=-1=>n=-1/2
2n+2=2=>2n=0=>n=0
2n+2=4=>2n=2=>n=1
2n+2=5=>2n=3=>n=3/2
2n+2=10=>2n=8=>n=4
2n+2=20=>2n=18=>n=9
Dar n este numar natural => n∈{0,1,4,9}