Calculated variables in `for` statement

Hi! I'm having trouble doing the following. I've been skulking around, but found no solace.

```
@each $a in (2, 3, 4) {
@for $b from 1 to $a {
property: calc($a + $b);
}
}
```
This correctly returns `property: 3` up until `property: 8`.

This, however, has trouble working as expected.
```
@each $a, $b in (1, 2, 3), (4, 5, 6) {
@for $c from 1 to ($a + $b) {
property: $c;
}
}
```
it is even possible? `calc($a + $b)` does not work either.