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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
OFFSET
1,1
COMMENTS
Primes p such that (p-1)*2^p+1 is also prime.
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.
Sequence in context: A266276 A088252 A334021 * A048979 A201363 A088332
KEYWORD
nonn
AUTHOR
STATUS
approved