@let {
  sumDigits ^(@sum @arr)
  drootl    &\@rangef [. sumDigits ^(\~>1 #@arr)]

  droot     ^(@last drootl)
  apers     ^(#-drootl)

  [
    !console.log "[number]: [digital root] [additive persistence] [intermediate sums]"
    ~@each [627615 39390 588225 393900588225]
      &n !console.log "{n}: {!droot n} {!apers n} {@str !drootl n}"
  ]
}