Determine the total number of semiprimes below 2023, that are immediately followed by an
emirp.
For example, 22 is a semiprime which is immediately followed by 23. But 23 is NOT an emirp, since 32 is composite.
List all valid pairs in conformity with the provisions of the problem.
*** Computer program/ excel solver aided methods are welcome, but a semi-analytic methodology is preferred.
(In reply to
re: semi-analytic solution by Charlie)
Right. I summed from 13, the first emirp. And, so, I compared with what Larry got in that range, which agrees with yours.
When I start at 3 to compare with your table, the approximation gives 14.01. It's the case that the estimates pp(y) and ps(y) break down at low y.
Edited on January 14, 2023, 11:16 am
re(2): semi-analytic solution
