Continuing to take advantage of the fact that R(15600) is now 30.09 %
factored I set up a search for primes of the form,

P = c * R(15600) / R(10) + 1 15600 digits.

with c consisting of 10 prime digits. We found two such c's:

c = 2255725272, 2255737522 .

c is repeated 1560 times with the final 2 becoming a 3.

David Broadhurst proved primalty.

These are by far the largest known primes with all prime digits. The
previous record was 3160 digits set in 1992.

Harvey Dubner