# Factor5

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Workload type |
TF |

First release |
5.03 |

Latest version |
2018-06-05 |

**Factor5** is a program that performs Trial factoring of Mersenne numbers. It is capable of trial factoring very large numbers, many billions of digits.

## About the program

Author: Luigi Morelli

The current version of Factor5 (and the previous versions Factor4, Factor3_2, and Factor3_1) are available here. The program performs trial factoring using multi-threaded processing. It can factor numbers with a hexillion digits or larger. Because it can work on such large numbers, it is used for Operation Billion Digits.

The program is run from the command line as follows:

- "factor <exponent> <start_bit> <stop_bit> <number of threads to use>"

All of the parameters are required, unless using the "--resume" switch.

## Known Limitations

- The routine can't be 100% safe on very small exponents (some factors may be skipped)
- There is no check for small bit-depth: M223 can be safely executed on bounds > 22 bits, M1009 can be executed on bounds > 20 bits and so on; the greater the exponent, the smaller the minimum bit depth allowed.