The OEIS is supported by the many generous donors to the OEIS Foundation.
Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.
Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.
%I #14 Jun 30 2013 03:03:44
%S 2,3,7,11,17,19,29,43,47,53,71,79,83,89,97,101,107,109,127,151,173,
%T 179,191,197,199,223,227,233,241,251,271,277,281,307,317,331,349,353,
%U 359,379,389,397,431,439,443,449,457,461,467,479,503,521,523,547,557,569
%N Primes p such that 2p - 1 and 2p + 1 are squarefree.
%H Paolo P. Lava, <a href="/A226993/b226993.txt">Table of n, a(n) for n = 1..1000</a>
%e 3 is in the sequence because 3 is prime and both 2*3 - 1 = 5 and 2*3 + 1 = 7 are squarefree.
%p with(numtheory); P:=proc(q) local n; for n from 1 to q do
%p if isprime(n) then if issqrfree(2*n-1) and issqrfree(2*n+1) then print(n)
%p fi; fi; od; end: P(10^5); #_Paolo P. Lava_, Jun 26 2013
%o (PARI) is(n)=isprime(n)&&issquarefree(2*n-1)&&issquarefree(2*n+1) \\ _Charles R Greathouse IV_, Jun 27 2013
%Y Cf. A005117.
%K nonn
%O 1,1
%A _Irina Gerasimova_, Jun 26 2013