This road sign is on the Christmas Circle roundabout in Borrego Springs, California.

The road sign says...

+---------------------+ | CA Hwy-79 23 | | County Airport 3 | | Salton Sea 30 | +---------------------+Finding road signs that contain at least three prime numbers each greater than 10 is non-trivial. These are called "triple prime road signs."

Off-by-one: If the 30 was 31, then this road sign would have four prime numbers with three of them greater than 10 (i.e. it would be a triple prime road sign).

the numbers are: 79 23 3 30 off-by-one math: (sqrt(79 - 30) - 3)! = 23 + 1 observe... 79 - 30 = 49 sqrt(49) = 7 7 - 3 = 4 4! = 4 * 3 * 2 * 1 = 24 forced triple primes: 79, 23, 13 = spf(30) + 3 observe... spf(30) = 2 + 3 + 5 = 10 10 + 3 = 13

**Creator:** Gerald Thurman
[gthurman@gmail.com]

**Created:** 21 December 2007

This work is licensed under a Creative Commons Attribution 3.0 United States License.