2147483647

This number is a prime.

2147483647 and 8191 are the only Mersenne prime numbers corresponding to a prime (31) and its reversal (13). [Loungrides]

M₃₁ = 2^31 - 1 = 0x7FFFFFFF. It also happens to be the largest signed 32-bit integer (available in many programing languages, i.e., C/C++ int on 32-bit platforms). [Zenczykowski]

The first prime that cannot be tested on 32-bit primality-check software. [Beedassy]

2147483647 = 46341 * 46341 - 4634*1. [Morgan]

2147483647 is the 63rd Fibonacci 31-step number; the 1st odd prime of this type. Note that 2^31-1 = 2147483647, making it the 8th Mersenne prime. [Loungrides]

The first Honaker number that is also a Mersenne prime. Can you find another? [Bajpai]