Numbers / 11

The Number 11

11 is prime: only 1 and 11 divide it evenly; the next prime after 11 is 13. 11's proper divisors total just 1, 10 short of 11, the deficient case most of 11's neighbors share too. 11 also carries: a palindrome, since 11 reads identically forwards and backwards; and a repunit built from 2 copies of the digit 1. 11 has a digit sum of 2; for 11, the digital root works out to 2. 11 shares no factor with 2-12; 11's own divisors start beyond that range. 11 is 1011 in binary and B in hex; as a Roman numeral it's XI.