I need to compute the following sum:
All that I have deduced is:
- Each term is divisible by $6$. So sum is is divisible by $6$.
- Sum is divisible by $5$ as 1st term is $1$ less than multiple of $5$ and second term is $1$ more than multiple of $5$. Next three terms are divisible by $5$. This cycle continues for every $5$ terms.
So sum will obviously be divisible by $30$.