Meme of a toucan. On the top panel its long beak labelled "M9999971879: is 2 to the power of 9999971879 minus 1, has 3010291492 decimal digits, and takes 2905663.125 GHz-Days to do one PRP (probable prime) test.
The bottom panel has a hand pulling away the long beak to reveal the toucan has a tiny human face underneath it, revealing it's divisible by the 11-digit number 19999943759 with a k value of 1.
(Context: For Mersenne numbers, which are of the form 2 to the power of p minus 1 where p is prime, if a Mersenne number composite, their factors will always take the form 2 times k times p minus 1. In this example, this really huge Mersenne number with over 3 billion digits only has an 11 digit factor because its k value is 1, in other words it's only double the p exponent plus 1, saving thousands of years of computation to do a more intensive probable prime test on it.)