Coresilience
= Coresilience
{title2=$C(n)$}
For an <integer> $n>1$, define $C(n)=(n-\varphi(n))/(n-1)$, the complementary proportion to the <resilience of a denominator>. For <composite numbers>, asking when this is a unit fraction is equivalent to the <divisibility> condition $n-\varphi(n)\mid n-1$.