2129
This number is a prime.
The smallest Sophie Germain prime that is also a strong prime with digits that alternate in parity.
2129 is the smallest Sophie Germain prime that is also a twin prime with digits that alternate in parity.
2129, when concatenated with the next 2 primes, is prime: 212921312137 is prime. [Noll]
2129 and its twin become prime when concatenated with the
composite number 9813 (21299813 and 21319813). [Chang]
2129 happens to be the next prime year that is the sum of three consecutive primes. [Richmond]
The smallest prime number that becomes a square when concatenated with its sum of digits. [Gaydos]
The smallest prime Q = 2129 that produces 10 primes from the
formula pi# + Q#/pi#, for i = 30, 92, 95, 161, 163, 164, 169,
278, 295 and 307. No other primorial is known that produces
more than 10 primes. Found by Jan van Delden. [Rivera]