Monday, February 22, 2016

modular arithmetic - How to calculate 21pmod10

I want to know how to compute the inverse of a number when the module is composite and the number is not coprime.



Can anyone give me the options with an example of how to compute with 2 ^ {-1} \pmod{10}?



Is there a way to do factorisation or some similar technique that ends with the same result like: 1/9 \pmod{10} = 1/3 \times 1/3 \pmod{10} and because 3 is comprime of 10 then is possible?



Thanks

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