@media (min-width: 0) {
  section li {
    $X:2;
    width: 100% * (1/$X);
  }
}
@media (min-width: 401px) {
  section li {
    $X:3;
    width: 100% * (1/$X);
  }
}

@media (min-width: 726px) {
  section li {
    $X:4;
    width: 100% * (1/$X);
  }
}
@media (min-width: 1001px) {
  section li {
    $X:5;
    width: 100% * (1/$X);
  }
}
@media (min-width: 1213px) {
  section li {
    $X:6;
    width: 100% * (1/$X);
  }
}

@mixin n-columns-min($width, $nCats){
  @media (min-width: $width){
    width: 100% * (1/$nCats);
  }
}

// @mixin n-columns-max($width, $nCats){
//   @media (max-width: $width){
//     width: 100% * (1/$nCats);
//   }
// }

section li {
  width: 100% * (1/2); // Default at Mobile

  @include n-columns-min(401px, 3);
  @include n-columns-min(726px, 4);
  @include n-columns-min(1001px, 5);
  @include n-columns-min(1213px, 6);

  // @import n-columns-max(401px, 3);
  // @import n-columns-max(726px, 4);
  // @import n-columns-max(1001px, 5);
  // @import n-columns-max(1213px, 6);
  //
  // width: 100% * (1/6); // Default at Desktop
}

Refactor mediaquery with @mixin and @include
Refactor mediaquery with @mixin and @include
