- **Math**
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- - **Probability of factor (TF)**
(*https://www.mersenneforum.org/showthread.php?t=15415*)

Probability of factor (TF)Hi,
Is there a formula / excel spreadsheet anywhere which lets me calculate the probablility that I find a factor for Mn by trial factoring from x to x+1 bits, with no previously known factor? Thanks, nugget |

[url]http://mersenne-aries.sili.net/credit.php[/url] (put in a TF assignment and factoring range, as part of the result it says the chance of finding a factor)
That's the easiest way, since it applies the formula for you. The actual formula is at: [url]http://www.mersenne.org/various/math.php[/url] [quote]the chance of finding a factor between 2[sup]X[/sup] and 2[sup]X+1[/sup] is about 1/x[/quote] Pretty simple. :smile: But note that this only counts starting at about log_2(p) bits, since all factors must be of the form 2kp+1. Whether there is a previously known factor does not make a difference in the distribution of further factors, but the TF depth does. |

[quote]the chance of finding a factor between 2X and 2X+1 is about 1/x[/quote]
That only applies if no prior factoring work has been done, which could have found a factor in that range. If that isn't the case, for example if a P-1 test has been done on the exponent, then the probability of finding a factor with TF will be less. |

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