/*REXX program  calculates and displays the  digital root  and  additive persistence.   */
say 'digital   additive'                         /*display the  1st  line of the header.*/
say "  root  persistence" center('number',77)    /*   "     "   2nd    "   "  "     "   */
say "═══════ ═══════════"   left('', 77, "═")    /*   "     "   3rd    "   "  "     "   */
say digRoot(       627615)
say digRoot(        39390)
say digRoot(       588225)
say digRoot( 393900588225)
say digRoot(89999999999999999999999999999999999999999999999999999999999999999999999999999)
say "═══════ ═══════════"   left('', 77, "═")    /*display the  foot separator.         */
exit 0                                           /*stick a fork in it,  we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
digRoot: procedure; parse arg x 1 z;  L= length(x)    /*get a number & also another copy*/
           do pers=1  until L==1;  $= left(x, 1)      /*sum until  digRoot ≡ one digit. */
              do j=2  for L-1;     $= $+substr(x,j,1) /*add digits in the decimal number*/
              end   /*j*/
           x= $;                      L= length(x)    /*a new num, it may be multi─digit*/
           end     /*pers*/
         return center(x, 7)  center(pers, 11)  z     /*return a nicely formatted line. */