sentences:  Perfect totient number
  
  In number theory, a perfect totient number is an integer that is equal to the sum of its iterated totients.That is, we apply the totient function to a number "n", apply it again to the resulting totient, and so on, until the number 1 is reached, and add together the resulting sequence of numbers; if the sum equals "n", then "n" is a perfect totient number.