1021 (another Prime Pages' Curiosity)
 Curios: Curios Search:   Participate: p = 1019 and 1021 are the largest known pair of twin primes where both p# + 1 and (p+2)# + 1 are primorial primes. The largest prime date in a common year falling exactly in between a prime number (71) of remaining days and a prime number (293) of elapsed days is October 21 or 10/21. Note that 71293 is prime. [Beedassy] The only prime formed from the concatenation of two semiprimes (10 and 21) whose prime factors consist of the four prime digits. [Silva] The only four-digit emirp pair whose reversals each occur on a 12-hour clock is 10:21 and its reversal. [Punches] Note that in the matrix product: ``` [ 1 0 ] [ 2 3 ] [ 2 3 ] = [ 2 1 ] [ 1 1 ] [ 5 7 ] ``` 1021 is prime, 2311 is prime, 2, 3, 5 and 7 are the first four primes (and incidentally, 2357 is prime). This is the only pair of 2-by-2 matrices with this property. [Hartley] The least prime > 11 whose digit sum equals the number of digits. [Hasler] The smallest prime whose sum of digits and digital length are squares. [Silva] The smallest concave-convex prime. [Pol] The smallest emirp which begins and ends with the same digit. [Silva] The smallest emirp containing three consecutive digits. [Loungrides] (There are 11 curios for this number that have not yet been approved by an editor.) Prime Curios! © 2000-2018 (all rights reserved)  privacy statement