Function compute 

fn compute<I>(
    input: &[i32],
    start: usize,
    upper: usize,
    nck: I,
    size: usize,
) -> [i32; 8]
where
    I: Iterator<Item = (i32, usize)>,

Quickly computes a digit taking advantage of the fact that the LCM is much smaller than the whole range.