a : 7 = x rest 4 =>a=7x+4 |+3
a : 15 = y rest 12=>a=15y+12 |+3
a : 20 = z rest 17=>a=20z+17 |+3
a+3 = 7(x+1)
a+3 = 15(y+1)
a+3 = 20(z+1)
7 = 7
15 = 3 × 5
20 = 2^2×5
---------------
c.m.m.m.c = 2^2×3×5×7 = 420
a+3 = 420
a = 420 - 3 = 417 (cel mai mic nr nat.)
