# Accumulation of numbers in loops in JavaScript

Let's use the loop to find the sum of integers from `1` to `100`. To solve such a problem, numbers are iterated over in loop and their sum is sequentially written to some variable:

`let res = 0; for (let i = 1; i <= 100; i++) { res = res + i; } console.log(res); // the required sum`

You can simplify the solution through the operator `+=`:

`let res = 0; for (let i = 1; i <= 100; i++) { res += i; } console.log(res);`

Find the sum of even numbers from `2` to `100`.

Find the sum of odd numbers from `1` to `99`.

Find the product of integers from `1` to `20`.

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