In terms of smaller numbers, there's M1347826279*M1552958761 (I TF'd both of them to make sure there were no small factors <10^21), but there's also some larger examples, such as MM61*MM89*MM107*MM127*MM521*MM607*...*MM82589933*..., going on as far as there are Mersenne Prime exponents to use, assuming that there are finitely many Mersenne primes (otherwise the resulting number is infinite). (2^2^((Loader's Number)↑↑↑...↑↑↑Loader's Number)+1)^2 (where the number of up arrows is Loader's number) is about as big as I can think of, and it's the square of a Fermat number, albeit a gargantuan one.
Last fiddled with by Stargate38 on 20210927 at 16:25
