A247952 Numbers k such that 2^k + 31 is prime.

4, 12, 36, 540, 844, 1192, 12136, 84280, 128356, 317464, 3018556

Offset

1,1

Comments

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

a(11) > 5*10^5. - Robert Price, Oct 25 2015

All terms are even. - Elmo R. Oliveira, Nov 25 2023

Links

Table of n, a(n) for n=1..11.

Henri Lifchitz and Renaud Lifchitz, Search for 2^n+31, PRP Top Records.

Formula

a(n) = 2*A262971(n). - Elmo R. Oliveira, Nov 25 2023

Mathematica

Select[Range[0, 10000], PrimeQ[2^# + 31] &]

Prog

(Magma) [n: n in [0..2000]| IsPrime(2^n+31)];
(PARI) is(n)=ispseudoprime(2^n+31) \\ Charles R Greathouse IV, May 22 2017

Crossrefs

Cf. A094076, A262971.

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).

Sequence in context: A140123 A164853 A076124 * A183923 A349053 A279277

Adjacent sequences: A247949 A247950 A247951 * A247953 A247954 A247955

Keyword

nonn,more

Author

Vincenzo Librandi, Sep 28 2014

Extensions

12136 and 84280 from Jens Kruse Andersen, Sep 29 2014

a(9)-a(10) (discovered by Lelio R Paula; see the Lifchitz link) added by Robert Price, Oct 04 2015

a(11) discovered by Robert Price, added by Elmo R. Oliveira, Nov 25 2023

Status

approved