English: This diagram shows the elements of the multiplicative group of integers modulo 10 ${\displaystyle (\mathbb {Z} /10\mathbb {Z} )^{\times }}$, also known as the Euler group, as a subgroup of the cyclic group of order 10. The neutral element of the cyclic group is on the right. The elements 1, 3, 7, 9 of the Euler group are shown by full circles.