Solution: doubly truncatable primes
73,331 This prime is the only such number. Tom Marlow will receive £20 for this ingenious contribution. Incidentally, he tells me that he now has a...
73,331
This prime is the only such number. Tom Marlow will receive £20 for this ingenious contribution. Incidentally, he tells me that he now has a special computer program that can factorise, or identify as prime, any number of up to 15 digits almost instantly.