Compute |U(4)|, |U(10)|, |U(40)|

I know that I have to compute the order of the group for each. Am I looking for |U(4)|=2, |U(10)|=4 and |U(40)|=10? as the answer?

Thanks in advance

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- July 1st 2009, 05:13 PMmathatlastAbstract Algebra- order of a group
Compute |U(4)|, |U(10)|, |U(40)|

I know that I have to compute the order of the group for each. Am I looking for |U(4)|=2, |U(10)|=4 and |U(40)|=10? as the answer?

Thanks in advance - July 1st 2009, 05:27 PMChris L T521
When ever you find the order of (same as ), we are always guaranteed to have 1 and n-1 in , so when .

In your case,

, so .

, so .

, so .

So two of your answers were correct.

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As an aside (if you see something like this in the future): If is a prime, then - July 1st 2009, 05:44 PMmathatlast
Thank you, Chris

- July 1st 2009, 06:23 PMBruno J.
And, just to add : more generally,