1237
This number is a prime.
The difference between 12372 and (1237 - 5)2 might surprise you.
An emirp formed from the number 12 and the 12th prime. Its reversal, 7321, is formed from the 21th prime and number 21. [Silva]
The smallest four-digit emirp with distinct digits. Note
that the sum of its digits is equal to the smallest
double-digit emirp. [Loungrides]
The first primeval emirp whose sum of digits is also an
emirp. Note that the number of primes contained is twice
its emirp sum of digits. [Beedassy]
The smallest "self-ranking prime" (primes which are a concatenation of n and prime[n]) that is also an emirp. [Green]
The first primeval number whose sum of digits is a different primeval number. [Lunsford]
The number of delegates needed to become the presidential nominee for the Republican Party of the United States of America. It is exactly half the number of total delegates, plus one.
The smallest distinct-digit "extra" center-deletable prime (emirp), i.e., deleting the central double-digit prime,
(23), another double-digit prime remains. [Loungrides]
Today (31 March 2018) the moon reached its fullest phase at 1237 GMT. In case you're curious, the next double Blue Moon will not occur until Halloween 2020.
1237 begins the largest case of three consecutive primes each with digits in strictly ascending order. [Gaydos]