login
A239742
Numbers k such that prime(k) * 2^k + 1 is prime.
2
1, 2, 3, 4, 5, 9, 12, 35, 78, 122, 276, 495, 715, 849, 927, 1128, 1263, 1418, 23201, 30316, 34894, 51844, 200821, 235383, 265970
OFFSET
1,2
COMMENTS
The PFGW program has been used to certify all the terms up to a(25), using a deterministic test which exploits the factorization of a(n)-1.
a(26) > 325000.
MATHEMATICA
Select[Range[1000], PrimeQ[Prime[#]* 2^# + 1] &]
PROG
(PARI) is(n, p=prime(n))=ispseudoprime(p<<n+1) \\ Charles R Greathouse IV, Jun 06 2017
CROSSREFS
Cf. A239741.
Sequence in context: A038201 A033084 A076134 * A101526 A264994 A331364
KEYWORD
nonn,more
AUTHOR
Giovanni Resta, Mar 26 2014
STATUS
approved