procedure digital_root(atom n, integer base=10)
integer root, persistence = 1
atom work = n
    while 1 do
        root = 0
        while work!=0 do
            root += remainder(work,base)
            work = floor(work/base)
        end while
        if root<base then exit end if
        work = root
        persistence += 1
    end while
    printf(1,"%15d root: %d persistence: %d\n",{n,root,persistence})
end procedure

digital_root(627615)
digital_root(39390)
digital_root(588225)
digital_root(393900588225)