How to calculate the sum of all values ​​in a loop?

Question

Sass

For example:

@for $i from 1 through 10
  $number: 121px * $i
    .box-#{$i}
      -width: $number

It will give 10 blocks with different widths. But how do you calculate the sum of all these widths?

Answer 1

Arithmetic progression, they should have been talking about it at school.
on scss:

$count: 10;
$baseWidth: 121px;

$sum: ($baseWidth + $baseWidth * $count) / 2 * $count;

result: