= Alwin Korselt
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<Alwin Korselt> is associated with <Korselt criterion> for <Carmichael numbers>. The criterion characterizes a composite <positive integer> $n$ by squarefreeness and the divisibilities $p-1\mid n-1$ for every <prime divisor> $p$ of $n$.
It turns a universal modular-exponent condition into a finite collection of arithmetic tests on <prime factors>. For example, $561=3\cdot11\cdot17$ is squarefree, and $2,10,16$ all divide $560$, giving the standard example of a <Carmichael number>.<Carmichael Numbers and Korselt's Criterion by Keith Conrad>[criterion and 561 example]{ref}
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