' FB 1.05.0 Win64

Function digitalRoot(n As UInteger, ByRef ap As Integer, base_ As Integer = 10) As Integer
  Dim dr As Integer
  ap = 0
  Do
    dr = 0
    While n > 0
      dr += n Mod base_
      n = n \ base_
    Wend
    ap += 1
    n = dr
  Loop until dr < base_
  Return dr
End Function

Dim As Integer dr, ap
Dim a(3) As UInteger = {627615, 39390, 588225, 393900588225}
For i As Integer = 0 To 3
 ap = 0
 dr = digitalRoot(a(i), ap)
 Print a(i), "Additive Persistence ="; ap, "Digital root ="; dr
 Print
Next
Print "Press any key to quit"
Sleep