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A196303 Numbers n such that both n and (n-1)*2^n+1 are primes. 0
2, 3, 7, 1471, 1483, 61627, 88731 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Primes p such that (p-1)*2^p+1 is also prime.

LINKS

Table of n, a(n) for n=1..7.

EXAMPLE

a(1)=2 because 2 and (2-1)*2^2+1=5 are both prime.

a(2)=3 because 3 and (3-1)*2^3+1=17 are both prime.

a(3)=7 because 7 and (7-1)*2^7+1=769 are both prime.

MATHEMATICA

Select[Prime[Range[9000]], PrimeQ[(#-1)2^#+1]&] (* Harvey P. Dale, Jan 19 2012 *)

PROG

(PARI) forprime(n=1, 1e4, if(ispseudoprime((n-1)<<n+1), print1(n", "))) \\ Charles R Greathouse IV, Oct 09 2011

CROSSREFS

Subsequence of A128001.

Cf. A029544, A196421, A196446.

Sequence in context: A238400 A266276 A088252 * A048979 A088332 A131959

Adjacent sequences:  A196300 A196301 A196302 * A196304 A196305 A196306

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Oct 02 2011

STATUS

approved

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Last modified April 20 14:27 EDT 2019. Contains 322310 sequences. (Running on oeis4.)