numerele care divid pe 15 sunt: 1,3,5 si 15
2x+1= 1, 2x= 0, x = 0
2x+1= 3, 2x= 2, x = 1
2x+1= 5, 2x= 4, x = 2
2x+1= 15, 2x= 14, x = 7