41 is Smallest Number whose Period of Reciprocal is 5

Theorem
$41$ is the first positive integer the decimal expansion of whose reciprocal has a period of $5$:
 * $\dfrac 1 {41} = 0 \cdotp \dot 0243 \dot 9$

Proof
From Reciprocal of $41$:
 * $\dfrac 1 {41} = 0 \cdotp \dot 0243 \dot 9$