# Tag Info

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### What is the difference between modulo and modulus?

"modulo" is an operator. For instance, we might say "19 and 64 are congruent modulo 5". "modulus" is a noun. It describes the 5 in "modulo 5". We might say "the modulus is 5". No, the two should ...

### modular multiplication

Here's a more compact and mathematical description of what is going on. Let $a$ and $b$ be the input, already reduced modulo $m$, so $a < m$ and $b < m$. (Code-wise, this means after the ...
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### Is the empty string of even length?

A number is even if it leaves no remainder when divided by two. Zero leaves no remainder when divided by two.
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### Calculating modulus of large non-factored numbers

The map from natural numbers to the ring of remainders is a homomorphism, which is a way to say that it has all sorts of nice properties with respect to operations +...

### how to calculate $2^{5000}$ mod 10 without calculator in fast way?

Consider the first few powers of 2: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024… Now take all of those mod 10: 1, 2, 4, 8, 6, 2, 4, 8, 6, 2, 4… Try to solve it yourself, from this, before ...
The idea behind Pollard $\rho$ is that if you take any function $f : [0, n - 1] \to [0, n - 1]$, the iteration $x_{k + 1} = f(x_k)$ must fall into a cycle eventually. Take now $f$ as a polynomial, and ...