500 < n < 1000
grupam , imparim , raman ,rest =9
c₁ , c₂ , c₃ caturi
n = 18· c₁ + 9 = 20 ·c₂ + 9 = 24·c₂ + 9 scadem 9
n -9 = 18· c₁ = 20 ·c₂ = 24 ·c₃
numarul ( n -9 ) = multiplu de 18 ; 20 si 24
18 = 2·3²
20 = 2² ·5
24 = 2³ · 3
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multiplu = 2³ · 3² · 5 = 8 · 9·5 = 360
n -9 = 360 ; n = 369 solutie falsa
360 ; 720 ; 1080 ,................ multiplii
n - 9 = 720
n = 729 elevi
