I recently had a question about Mersenne primes. After getting the question wrong and looking up what they were I discovered an error in the question.
The question was:
What is the first Mersenne prime over 1000?
The answer given was 1279.
A Mersenne prime is a prime that is 1 less than a power of 2. 1280 is not a power of two.
The question should read instead: What is the first exponent over 1000 that results in a Mersenne prime?