droot: function [num][
    persistence: 0
    until [
        num: sum to [:integer] split to :string num
        persistence: persistence + 1
    ][ num < 10 ]
    return @[num, persistence]
]

loop [627615, 39390, 588225, 393900588225] 'i [
    a: droot i
    print [i "has additive persistence" a\0 "and digital root of" a\1]
]