# Number Gossip

(Enter a number and I'll tell you everything you wanted to know about it but were afraid to ask.)

## Unique Properties of 19

• 19 is the side length of the Go board
• 19 is the largest prime which is a palindrome in Roman numerals
• 19 is the smallest number n such that nn is pandigital (contains all 10 digits)
• 19 is the smallest prime which when turned upside down yields a different prime (61)
• 19 is the smallest prime with a digital root of 1
• The 19th Fibonacci number is the smallest composite Fibonacci number with a prime index
• 19 is the smallest prime that has the same digit sum as its square
• A hexahexaflexagon is made from a strip consisting of 19 equilateral triangles
• 19 is the only number n for which there is no multi-digit palindrome whose digit sum and beginning are both n
• 19 is the smallest prime whose reversal is composite
• 19 is the only prime which is equal to the difference of two cubes of primes
• 19 is the maximum number of 4th powers needed to sum to any positive integer
• 19 is the smallest number that is equal to the product of its digits plus the sum of its digits
• The second repunit prime has 19 digits
• 19 is the smallest prime ending in a composite digit
• 19 is the smallest number sandwiched between two numbers that are products of 3 primes