Amount concentration versus number concentration
The "amount" of a substance is the proper term for the "number of moles" (Wikipedia; Gold Book). So, the two quantities are related by a factor of the Avogadro constant, $\pu{6.022\times 10^23 mol-1}$.

If you have $\pu{1 mol}$ of helium in a $\pu{1 m3}$ box, the amount concentration is $\pu{1 mol m-3}$, or $\pu{0.001 mol dm-3}$ if you prefer those units.

The corresponding number concentration is $\pu{6.022\times 10^23 m-3}$.