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
semi-analytic solution by Steven Lord)
If palindromes are included we get these 15:
4 2 2 5 5
6 2 3 7 7
10 2 5 11 11
106 2 53 701 107
166 2 83 761 167
178 2 89 971 179
346 2 173 743 347
358 2 179 953 359
382 2 191 383 383
982 2 491 389 983
1282 2 641 3821 1283
1438 2 719 9341 1439
1486 2 743 7841 1487
1522 2 761 3251 1523
1618 2 809 9161 1619
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Posted by Charlie
on 2023-01-14 11:05:15 |
re: semi-analytic solution
