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 A057221 Numbers k such that 2^k + 19 is prime. 18
 2, 6, 30, 162, 654, 714, 1370, 1662, 1722, 2810, 77142, 156254, 432974, 1092242, 1245230 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(14) > 5*10^5. - Robert Price, Aug 27 2015 All terms are even. - Robert Israel, Aug 28 2015 For numbers k in this sequence, the number 2^(k-1)*(2^k+19) has deficiency 20 (see A223607). - M. F. Hasler, Jul 18 2016 LINKS Table of n, a(n) for n=1..15. Henri Lifchitz and Renaud Lifchitz (Editors), Search for 2^n+19, PRP Top Records. FORMULA a(n) = 2*A253774(n). - Joerg Arndt, Aug 28 2015 MAPLE select(n -> isprime(2^n+19), [seq(2*i, i=1..10000)]); # Robert Israel, Aug 28 2015 MATHEMATICA Do[ If[ PrimeQ[ 2^n + 19 ], Print[ n ] ], {n, 1, 15000} ] Select[Range[10000], PrimeQ[2^# + 19] &] (* Vincenzo Librandi, Aug 28 2015 *) PROG (Magma) [n: n in [0..1000] | IsPrime(2^n+19)]; // Vincenzo Librandi, Aug 28 2015 (PARI) for(n=1, 9e9, ispseudoprime(2^n+19)&&print1(n", ")) \\ M. F. Hasler, Jul 18 2016 CROSSREFS Cf. A223607, A253774. Cf. A019434 (primes 2^k+1), A057732 (2^k+3), A059242 (2^k+5), A057195 (2^k+7), A057196(2^k+9), A102633 (2^k+11), A102634 (2^k+13), A057197 (2^k+15), A057200 (2^k+17), this sequence (2^k+19), A057201 (2^k+21), A057203 (2^k+23). Sequence in context: A218940 A005432 A009422 * A180892 A366266 A196497 Adjacent sequences: A057218 A057219 A057220 * A057222 A057223 A057224 KEYWORD nonn,more AUTHOR Robert G. Wilson v, Sep 17 2000 EXTENSIONS a(11)-a(13) from Robert Price, Aug 27 2015 Edited by M. F. Hasler, Jul 18 2016 a(14)-a(15) found by Stefano Morozzi, added by Elmo R. Oliveira, Nov 19 2023 STATUS approved

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Last modified September 13 20:16 EDT 2024. Contains 375910 sequences. (Running on oeis4.)