This number is a prime.
David MacQuarrie's PrimeTimeClock will only display the time (as hours:minutes:seconds) if the corresponding number is prime. It displays 7669 different times each day and indicates whether a prime is special (e.g., a Sophie Germain prime) by illuminating its beacon in different colors.
The number of twin lucky numbers less than a million. [Schneider]
The number of primes that can appear on a 24-hour digital clock displaying hours, minutes, seconds (00:00:00 up to 23:59:59). [Gupta]