# Tag Info

### Why doesn't Shor's algorithm output a solution for some numbers?

What you should have seen in texts is the statement that you have to pick $a$ at random from the numbers that are coprime to $N$. There are then certain claims about the order, $r$ that you get: with ...
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### Why doesn't Shor's algorithm output a solution for some numbers?

If $f(x) = a^x \pmod{N}$ passes through $-1$, that value of $a$ won't work. For example, $a=2$ fails for $N=33$ because $2^5 = 32 \equiv -1 \pmod{33}$. This should have been mentioned in whatever ...
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1 vote

### I have question about cost of 'modular multiplication unitary' in Shor's algorithm

The point is that you can perform this calculation efficiently on a classical computer. So you can implement the same algorithm on a quantum computer. Just think: if you had to do this calculation by ...
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