Prime Factors Calculator

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This calculator will calculate the prime factors of a positive integer. The algorithm used can, in theory, handle very large numbers but beware that numbers with large prime factors could take a long time to factorise. For example, 1234567890123456789012345678901234567890 factorises almost instantly, whereas 12345678901234567 takes a lot longer, because, even though smaller, one of the prime factors is a large number.

The old Java applet version of this page is available here.


Number to factorise:




This page uses Tom Wu's JSBN library. Please see the JSBN licence here


Whilst I try to keep the information on this site accurate, I'm only human and I do occasionally make mistakes. I therefore advise you to check any information before using it for anything important. If you do find any errors, please let me know so that I can correct them.

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This page was last changed on: 02 August 2021.

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