show that only one out of a,a+2 and a+4 is divisible by 3
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A number is divisible by 3 if and only if sum of its digits is divisible by 3
So, if a is divisible by 3,
a+2 cannot be divisible as sum of digits cannot be divisible by 3 as 2 is not divisible by 3
a+4 cannot be divisible as sum of digits cannot be divisible by 3 as 4 is not divisible by 3
if a+2 is divisible by 3,
a cannot be divisible as sum of digits cannot be divisible by 3 as 2 is not divisible by 3
a+4 cannot be divisible as sum of digits cannot be divisible by 3 as 4 is not divisible by 3
if a+4 is divisible by 3,
a+2 cannot be divisible as sum of digits cannot be divisible by 3 as 2 is not divisible by 3
a cannot be divisible as sum of digits cannot be divisible by 3 as 4 is not divisible by 3
So, if a is divisible by 3,
a+2 cannot be divisible as sum of digits cannot be divisible by 3 as 2 is not divisible by 3
a+4 cannot be divisible as sum of digits cannot be divisible by 3 as 4 is not divisible by 3
if a+2 is divisible by 3,
a cannot be divisible as sum of digits cannot be divisible by 3 as 2 is not divisible by 3
a+4 cannot be divisible as sum of digits cannot be divisible by 3 as 4 is not divisible by 3
if a+4 is divisible by 3,
a+2 cannot be divisible as sum of digits cannot be divisible by 3 as 2 is not divisible by 3
a cannot be divisible as sum of digits cannot be divisible by 3 as 4 is not divisible by 3
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