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%I #32 Sep 02 2019 15:04:03
%S 2,3,5,53,189,293,1107,2181,2695,2871,7667,19999,27471,44537,62323,
%T 134367,174295
%N Exponents k for which reversal(2^k-1) is prime.
%C According to the statements in the first link given below, the terms for k <= 7667, the primes of the form reversal(2^k-1) are certified and for k >= 19999 they are probable primes.
%H Carlos Rivera, <a href="https://www.primepuzzles.net/puzzles/puzz_417.htm">Puzzle 417</a>.
%H Chris K. Caldwell and G. L. Honaker, <a href="https://primes.utm.edu/curios/page.php?number_id=7267&submitter=Rivera">Prime Curio for 1990474529917009</a>.
%e 5 is included because for n=5, reversal(2^5-1)=13 is prime.
%t Select[Range[7667], PrimeQ[IntegerReverse[2^# - 1]] &]
%o (PARI) isok(k) = isprime(fromdigits(Vecrev(digits(2^k-1)))); \\ _Michel Marcus_, Aug 10 2019
%Y Cf. A000225, A000668, A001348, A000079, A000043, A057708, A134037, A134038, A134039.
%K nonn,base,more
%O 1,1
%A _Metin Sariyar_, Aug 09 2019
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