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 A247952 Numbers n such that 2^n + 31 is prime. 4
 4, 12, 36, 540, 844, 1192, 12136, 84280, 128356, 317464 (list; graph; refs; listen; history; text; internal format)
 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 LINKS Henri & Renaud Lifchitz, PRP Records, search for 2^n+31 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. numbers n such that 2^n+k is prime: (0,1,2,4,8,16) for k=1; A057732 (k=3), A059242 (k=5), A057195 (k=7), A057196 (k=9), A102633 (k=11), A102634 (k=13), A057197 (k=15), A057200 (k=17), A057221 (k=19), A057201 (k=21), A057203 (k=23), A157006 (k=25), A157007 (k=27), A156982 (k=29), this sequence (k=31), A247953 (k=33), A220077 (k=35). Sequence in context: A140123 A164853 A076124 * A183923 A279277 A101555 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 STATUS approved

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Last modified July 15 20:24 EDT 2019. Contains 325056 sequences. (Running on oeis4.)