0023

Twenty-three is the ninth prime number, the smallest odd prime that is not a twin prime.It is, however, a cousin prime with 19, and a sexy prime with 17 and 29; while also being the largest member of the first prime sextuplet (7, 11, 13, 17, 19, 23). Twenty-three is also the next to last member of the first Cunningham chain of the first kind (2, 5, 11, 23, 47), and the sum of the prime factors of the second set of consecutive discrete semiprimes, (21, 22). 23 is the smallest odd prime to be a highly cototient number, as the solution to x − ϕ ( x ) {\displaystyle x-\phi (x)} for the integers 95, 119, 143, and 529.