It doesn't make sense to ask for the sum of just one thing.
This is like asking what the sum of 1 is. Or what the sum of a tv is. Well, the sum of 1 is in fact 1. So technically, the answer to your question would be:
a 50 side shape
pentadecahedron
A shape does not have a sum. The angles of a shape have a sum, the lengths of its sides have a sum, the number of its diagonals are a sum, but the shape itself certainly does not have any sum!
A shape does not have a sum. You can sum its angles, the lengths of its sides, the areas of its faces and so on. But the shape does not have a sum, in itself.
Sum of 50 and 47 is 97.
50.
89
The sum of all the sides of a given shape is the perimeter of that shape.
100.
zero
The sum of the first 50 whole numbers is 1,225.
The sum of the first 50 natural numbers is 1,251.
51