n:9=c1 rest 3, n=9c1+3, n-3=9c1
n:18=c2 rest 3, n=18c2+3, n-3=18c2
n:27=c3 rest 3, n=27c3+3, n-3=27 c2
adica n-3= M [9,18, 27]
calculez [9,18,27]
9=3^2
18=2*3^2
27=3^3
[9,18,27]=2*3^3=2*27=54
n-3= M 54=k*54
dar se cere cel mai mic nr cu aceasta proprietate deci k=1
adica n-3=54, n=54+3
n=57 este nr cautat