a : 15 = x rest 3 ==> a = 15x+3
a : 30 = y rest 3 ==> a = 30y+3
a : 45 = z rest 3 ==> a = 45z + 3
15 = 3 × 5
30 = 2 × 3 × 5
45 = 3^2 × 5
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a = 2 × 3^2 × 5 + 3 = 90+3 = 93 (numarul cautat)
93 : 15 = 6 rest 3
93 : 30 = 3 rest 3
93 : 45 = 2 rest 3