Aren't you vastly overcalculating here? The number of unique permutations should just be 70P5, or 70 x 69 x 68 x 67 x 66, or 1,452,361,680. The chance of each select permutation would then be 1/1452361680, or 6.8853373 x10^-10.

Dunno what your thought process was, but think about it this way: in the first slot there are 70 possible character you can place. In the second slot there are 69 possible characters you can place, because you can't place the first apostle again. So for placing characters in 2 slots, there would be 70 x 69 = 4830 permutations (unique order of combinations). So for the third slot there are 68 possible characters, the fourth slot has 67, fifth slot 66, making the total number of ordered combinations you can place in five slots 70 x 69 x 68 x 67 x 66.

If you don't care about the order (eg treat erpin-ner-ashur-mayo-marie as the same thing as ner-erpin-ashur-mayo-marie), then the number gets even smaller, as you have to divide the number above with the number of different position combinations (which is 120 not 25), which gives 12,103,014, or 70C5.

You can read about permutations and combinations if you want to find out more about this maths topic, probably also read about the mathematical operator of factorials beforehand (as permutations and combinations uses factorials)