Sacred number

From Warhammer 40k

Sacred Numbers were introduced back in 2nd Edition 40k, and each of the four main Chaos Gods had one. In game terms, a unit of 'regular' Chaos Space Marines with the sacred number, or multiple thereof (as Chaos Space Marines can utilise squads of up to 20, rather than the 10 of the loyalists), of models in it received a free Aspiring Champion upgrade for the unit. This rule, and largely the accompanying fluff, was dropped in later editions due - among other reasons - to the fact that it tended to unbalance certain forces (Slaaneshi units only being 6-strong, when they're already considered the 'weakest' of the four, for example).

Slaanesh's sacred number was 6, Nurgle's was 7, Khorne's was 8 and Tzeentch's was 9.

Many players still use the sacred numbers for squad sizes in their fluff, but obviously don't apply the 'free Champion' rule.