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%I #38 Nov 27 2023 15:07:58
%S 4,12,36,540,844,1192,12136,84280,128356,317464,3018556
%N Numbers k such that 2^k + 31 is prime.
%C Some terms correspond to probable primes. Lifchitz link shows Paul Underwood discovered 84280, and Lelio R Paula found 128356 and 317464 are in the sequence. - _Jens Kruse Andersen_, Sep 29 2014
%C a(11) > 5*10^5. - _Robert Price_, Oct 25 2015
%C All terms are even. - _Elmo R. Oliveira_, Nov 25 2023
%H Henri Lifchitz and Renaud Lifchitz, <a href="http://www.primenumbers.net/prptop/searchform.php?form=2^n%2B31">Search for 2^n+31</a>, PRP Top Records.
%F a(n) = 2*A262971(n). - _Elmo R. Oliveira_, Nov 25 2023
%t Select[Range[0,10000], PrimeQ[2^# + 31] &]
%o (Magma) [n: n in [0..2000]| IsPrime(2^n+31)];
%o (PARI) is(n)=ispseudoprime(2^n+31) \\ _Charles R Greathouse IV_, May 22 2017
%Y Cf. A094076, A262971.
%Y Cf. Numbers k such that 2^k + d is prime: (0,1,2,4,8,16) for d=1; A057732 (d=3), A059242 (d=5), A057195 (d=7), A057196 (d=9), A102633 (d=11), A102634 (d=13), A057197 (d=15), A057200 (d=17), A057221 (d=19), A057201 (d=21), A057203 (d=23), A157006 (d=25), A157007 (d=27), A156982 (d=29), this sequence (d=31), A247953 (d=33), A220077 (d=35).
%K nonn,more
%O 1,1
%A _Vincenzo Librandi_, Sep 28 2014
%E 12136 and 84280 from _Jens Kruse Andersen_, Sep 29 2014
%E a(9)-a(10) (discovered by Lelio R Paula; see the Lifchitz link) added by _Robert Price_, Oct 04 2015
%E a(11) discovered by Robert Price, added by _Elmo R. Oliveira_, Nov 25 2023
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