In traditional mathematics, an integer divisible only by 1 and itself.
Known to drive mathematicians mad searching for the next largest one - computers all over the world are continually searching. At the time of writing, the largest prime found was 12978189 digits in length.
1 is prime.
3 is prime.
7 is prime.
A joke in mathematical circles about the properties of induction goes something like:
Base case: 1 is prime
K+1 case: 3 is prime
Therefore all odd numbers are prime. QED
The joke being, of course - that due to faulty logic in the proof
, the conclusion is that all odd numbers are prime - a clear fallacy (example: 21... 7*3=21 so 21 is NOT prime).