43112609

This number is a prime.

The largest known Mersenne prime exponent (as of 23 August 2008): see 2^43112609-1.

Mersenne prime M47, i.e. 2^43112609-1 contains the exponent of (the larger) Mersenne prime M50, i.e., 77232917. [Harrison]

The largest Mersenne prime exponent such that changing every digit n with 2^n-1 yields a prime. [Sariyar]