The hardware and software on this system was updated September 4th.
Please let me know of any problem you encounter.
731 is composite, being the product of the primes 17 and 43, but 7331, 73331, 733331 and 7333331 are all prime. This is the only three-digit composite with this property.
The largest composite number such that deleting any
digit(s) will never yield another composite number, i.e.
only yields primes or 1. [Hasler]