100a + 10b +c + 100b +10c +a + 100c + 10a +b = 999
111a +111b +111c = 999 / : 111
a+b+c = 9 a,b,c =1,2,3.... , 9
a 1 1 1 1 1 2 2 2
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b 2 3 4 5 6 1 3 4
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c 6 5 4 3 2 6 4 3
126 , 136, 144, 135, 144 , 153 , .......