Self number
A NATURAL NUMBER THAT CANNOT BE WRITTEN AS THE SUM OF ANY OTHER NATURAL NUMBER N AND THE INDIVIDUAL DIGITS OF N
Colombian number; Columbian number; Self-number; Self prime; Devlali number
In number theory, a self number or Devlali number in a given number base b is a natural number that cannot be written as the sum of any other natural number n and the individual digits of n. 20 is a self number (in base 10), because no such combination can be found (all n < 15 give a result less than 20; all other n give a result greater than 20).