Random Number Generation 1-100 odds

I have a random number generator that I am trying to prove is "broken". It randomly generates numbers from 1 to 100. However in 50 attempts, it has not generated a single number over 85. So I guess the question is, __what are the odds of randomly generating a number (1-100) 50 times in a row and never generating a numbers 86 through 100__?

On the programming end, there's 4 catagories; like 1-60 produces a D, 61-85 produces a C, 86-95 produces a B, and 96-100 produces an A. And B or A are NEVER generating. So I'm trying to figure out if it was a QA test, are the odds of this happening outstanding enough that the programming end should be looked into .

Thanks everyone for your help in advance.