Sum of Integers from 1 to n

What does the sum of integers from 1 to $n$ mean?

Natural numbers are positive numbers starting from $1$. These can be written as:

$1,2,3,4,5,6,7,8,9,10......$

We want to write a program that takes a number and sums up all the numbers from $1$ up to that number.

For example, if $n = 5$, then the sum of numbers from $1$ to $5$ is: $1 + 2 + 3 + 4 + 5 = 15$.

Mathematical Notation

The sum of all numbers up to a number is equal to the sum of that number and the sum of all the numbers before it. Let’s write it down mathematically:

$\sum_{i=1} ^{5} i$

$=$ $5$ ...