Mathematical Approach

Creatures with prime converted mana costs get
+1/+1. (2,3,5 and 7 are prime.)
"Biomocular newtonian prime equations are simple -
just a matter of taking the seventeenth square root
of the fifteenth integer and dividing it by the total sum
of the cube roots of 178x, then carrying the three."
- Sir Arthur Beech, Theorist