So i'm assuming 33^a is saying any number that is a square of 33 inside of 1,313 so first, to find how many even numbers divide 1,313 by two to get 656.5 so if I am not mistaken 656 numbers in 1,313 will be even. Now find all squares of 33 that don't pass 1,313 which is 33 itself and 1,089 because 33^3 is 35,937 so add 2 to 656 to get 668. so the probability is 658/1,313 i believe.
