Possible Duplicate:
How do I prove $n$ is a Carmichael number?
I am trying to verify the fact that $1729$ is a Carmichael number. However, a number $n$ is a carmichael number if and only if $a^{n-1} \equiv 1 \pmod n$ for all $a$ that are relatively prime to $n$. Is there any more efficient way of showing that it is a carmichael number short of testing all of the numbers that are relatively prime to $1729$?