Generated by SassMeister.com.

input.scss

 @for $i from 1 through 24 {
    &--size-#{$i} {
      grid-column: calc((25 - #{$i}) /2) / span #{$i};
      grid-row:  calc((25 - #{$i}) / 2) / span #{$i};
    }
  }

output.css

.foo--size-1 {
  grid-column: calc((25 - 1) /2)/span 1;
  grid-row: calc((25 - 1) / 2)/span 1;
}

.foo--size-2 {
  grid-column: calc((25 - 2) /2)/span 2;
  grid-row: calc((25 - 2) / 2)/span 2;
}

.foo--size-3 {
  grid-column: calc((25 - 3) /2)/span 3;
  grid-row: calc((25 - 3) / 2)/span 3;
}

.foo--size-4 {
  grid-column: calc((25 - 4) /2)/span 4;
  grid-row: calc((25 - 4) / 2)/span 4;
}

.foo--size-5 {
  grid-column: calc((25 - 5) /2)/span 5;
  grid-row: calc((25 - 5) / 2)/span 5;
}

.foo--size-6 {
  grid-column: calc((25 - 6) /2)/span 6;
  grid-row: calc((25 - 6) / 2)/span 6;
}

.foo--size-7 {
  grid-column: calc((25 - 7) /2)/span 7;
  grid-row: calc((25 - 7) / 2)/span 7;
}

.foo--size-8 {
  grid-column: calc((25 - 8) /2)/span 8;
  grid-row: calc((25 - 8) / 2)/span 8;
}

.foo--size-9 {
  grid-column: calc((25 - 9) /2)/span 9;
  grid-row: calc((25 - 9) / 2)/span 9;
}

.foo--size-10 {
  grid-column: calc((25 - 10) /2)/span 10;
  grid-row: calc((25 - 10) / 2)/span 10;
}

.foo--size-11 {
  grid-column: calc((25 - 11) /2)/span 11;
  grid-row: calc((25 - 11) / 2)/span 11;
}

.foo--size-12 {
  grid-column: calc((25 - 12) /2)/span 12;
  grid-row: calc((25 - 12) / 2)/span 12;
}

.foo--size-13 {
  grid-column: calc((25 - 13) /2)/span 13;
  grid-row: calc((25 - 13) / 2)/span 13;
}

.foo--size-14 {
  grid-column: calc((25 - 14) /2)/span 14;
  grid-row: calc((25 - 14) / 2)/span 14;
}

.foo--size-15 {
  grid-column: calc((25 - 15) /2)/span 15;
  grid-row: calc((25 - 15) / 2)/span 15;
}

.foo--size-16 {
  grid-column: calc((25 - 16) /2)/span 16;
  grid-row: calc((25 - 16) / 2)/span 16;
}

.foo--size-17 {
  grid-column: calc((25 - 17) /2)/span 17;
  grid-row: calc((25 - 17) / 2)/span 17;
}

.foo--size-18 {
  grid-column: calc((25 - 18) /2)/span 18;
  grid-row: calc((25 - 18) / 2)/span 18;
}

.foo--size-19 {
  grid-column: calc((25 - 19) /2)/span 19;
  grid-row: calc((25 - 19) / 2)/span 19;
}

.foo--size-20 {
  grid-column: calc((25 - 20) /2)/span 20;
  grid-row: calc((25 - 20) / 2)/span 20;
}

.foo--size-21 {
  grid-column: calc((25 - 21) /2)/span 21;
  grid-row: calc((25 - 21) / 2)/span 21;
}

.foo--size-22 {
  grid-column: calc((25 - 22) /2)/span 22;
  grid-row: calc((25 - 22) / 2)/span 22;
}

.foo--size-23 {
  grid-column: calc((25 - 23) /2)/span 23;
  grid-row: calc((25 - 23) / 2)/span 23;
}

.foo--size-24 {
  grid-column: calc((25 - 24) /2)/span 24;
  grid-row: calc((25 - 24) / 2)/span 24;
}

settings.json

{
  "sass": {
    "compiler": "Ruby Sass/3.7.4",
    "extensions": {},
    "syntax": "SCSS",
    "outputStyle": "expanded"
  },
  "autoprefixer": false
}