If you want to know where the next Mersenne prime number might be, then you could find it here
The 51st known Mersenne prime was discovered on December 7, 2018. It is: Source: https://www.mersenne.org.
On December 26, 2017, the 50th known Mersenne prime was found: 2 raised to a power of 77232917-1. This number contains 23249425 digits if written in the decimal system. It is the largest currently known prime number. The discoverer is Jonathan Pace, an electrical engineer from Germantown Tennesse, USA. More info: http://www.mersenne.org