This Sass (SCSS) function utilises the Greated Common Divisor (gcd) to reduce duplicate styles.

gcd_sass_script.scss

// Algorithm to calculate the Lowest Common Denominator
@function gcd($a, $b){
  @if $b == 0 {
    @return $a;
  } @else {
    @return gcd($b, $a%$b);
  }
}

// Example Use-case:

//
// Mass generate classes for each percentage without duplicates
//
@for $i from 2 through 10 {
  @for $ii from 1 to $i {
    @if gcd($i,$ii) == 1 {
      $percent: percentage(1/$i);
      $fraction: #{$ii}-#{$i};

      .col-#{$fraction} {
        @extend %column;
        width: get_width($amount);
      }
    }
  }
}

//
//  Outputs to css
//
//  .col-1-2 { width: 50%; }
//  .col-1-3 { width: 33.3333333%; }
//  .col-2-3 { width: 66.6666666%; }
//  .col-1-4 { width: 25%; }
//  .col-2-4 { width: 50%; } <-- Doesn't get created
//  .col-3-4 { width: 75%; }
//  .col-1-5 { width: 20%; }
//  .col-2-5 { width: 40%; }
//  .col-3-5 { width: 60%; }
//  .col-4-5 { width: 80%; }
//  .col-1-6 { width: 16.6666666%; }
//  .col-2-6 { width: 33.3333333%; } <-- Doesn't get created
//  [etc...]
//

Why @if gcd($i,$ii) == 1 ? The value of returned by gcd($i, $ii) is different depend on the two values, not only 1. Explain please. Thanks.