SUB digitalroot (what)
    LET dr = ABS(what)
    IF dr > 10 THEN
       LET ap = 0
       DO
          LET ap = ap + 1
          DO WHILE dr <> 0
             LET t = t + REMAINDER(dr, 10)
             LET dr = IP(dr / 10)
          LOOP
          LET dr = t
          LET t = 0
       LOOP WHILE dr > 9
    END IF
    PRINT what, "Additive persistance ="; ap, "Digital root ="; dr
END SUB

CALL digitalroot (627615)
CALL digitalroot (39390)
CALL digitalroot (588225)
CALL digitalroot (393900588225)
END