A283191 Prime numbers p > 2 such that (2^p - 5)/3 is prime.

7, 13, 19, 31, 373, 811, 1117, 5059, 12601

Offset

1,1

Comments

Let W = (2^p - 5)/3 and s = (W+1)/(2*p), then 5^s == 2 (mod W) for terms 1..9.

Subsequence of 7, 13, 19, 31, 51, 55, 85, 111, 319, 373,.. which are numbers m such that (2^m-5)/3 is prime. - R. J. Mathar, Mar 05 2017

Links

Table of n, a(n) for n=1..9.

Mathematica

Select[Prime@ Range[2, 1000], PrimeQ[(2^# - 5)/3] &] (* Michael De Vlieger, Mar 03 2017 *)

Prog

(PARI)
forprime(p=3, 30000, W= (2^p-5)/3; if(ispseudoprime(W), print1(p, ", ")))

Crossrefs

Cf. A000978.

Sequence in context: A023255 A122482 A265629 * A048375 A198035 A208720

Adjacent sequences: A283188 A283189 A283190 * A283192 A283193 A283194

Keyword

nonn,more

Author

Dmitry Ezhov, Mar 02 2017

Status

approved