Numbers / 55

The Number 55

55 is composite: factorization 5 × 11. That gives 55 exactly 4 divisors: 1, 5, 11, 55. 55's proper divisors total just 17, 38 short of 55, the deficient case most of 55's neighbors share too. 55 also carries: the 10th triangular number, the sum of 1 through 10; and a Fibonacci number, since 34 + 21 = 55; and a palindrome, since 55 reads identically forwards and backwards. 55 has a digit sum of 10; for 55, the digital root works out to 1. 55: 5, 11 all divide 55 evenly, out of 2-12. 55 is 110111 in binary and 37 in hex; as a Roman numeral it's LV.