Prove that `2. 7^n+3. 5^n-5`is divisible by 24, for all `n in N`.

Explanation

Given expression is.

`2*7^n+3*5^n-5`

When `n = 1`, given expression is,

`2*7+3*5-5 = 12+15-5 = 24`

So, for `n=1`, given expession is divisible by `24`.

Let for any `k in N`, given expression is divisible by `24`.

Then, `2*7^k+3*5^k-5 = 24c`, where `c` is a natural number.

`=>3*5^k = 24c-2*7^k+5->(1)`

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