I understand how to do summation notation and the formula for it (n(n+1))/2 and how that differs if n has an exponent in it, but what if you're asked to rewrite a problem in summation notation?

For example "Rewrite 1+2+3...+100 in summation notation"

and just so I have a clear understanding let's also say

"Rewrite 1^2+2^2+3^2...+100^2 in summation notation"

Thanks in advance!