The simple purity of mathematics tells us that:
pow(1.212, 5) = 2.615249328
which rounds to 2.6
IE IEC 60063 tells us that it rounds to 2.7
So instead of a simple, elegant mathematical formula I need to use table look ups to generate and verify random standard resistance values.
Okay, I'm done for now.
EDIT: I am assuming that there is some physical aspect to this that I do not know, something in the manufacturing process, materials proportions, or the like that makes this case.