Prime numbers are used for secret writings (cryptography ...
If this seems a mere coincidence, then all doubts should be removed once we realize that joining these 7, 29, and 139 numbers left-to-right 729139 or right-to-left 139297 also produces in both cases primes with prime digit sums (7+2+9+1+3+9= 31) making them additive prime numbers too!Do you know how rare prime numbers are let alone additive prime numbers?