%I #23 Sep 08 2022 08:45:17

%S 1,3,5,9,11,15,21,23,29,33,35,39,41,51,53,63,65,69,75,81,83,89,95,99,

%T 105,111,113,119,125,131,135,141,153,155,165,173,179,183,189,191,209,

%U 215,219,221,231,233,239,243,245,249,251,261,273,281,285,293,299

%N Odd n such that 2*n+1 is prime.

%C Also: Numbers k such that 2k+1 is in A002145, i.e., a Gaussian prime. - _M. F. Hasler_, Feb 25 2011

%C Also: Number of quadratic residues modulo A002145(n). - _M. F. Hasler_, Feb 25 2011

%H G. C. Greubel, <a href="/A104635/b104635.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = floor(A002145(n)/2). - _M. F. Hasler_, Feb 25 2011

%t Select[Range[1,301,2],PrimeQ[2#+1]&] (* _Harvey P. Dale_, May 08 2012 *)

%o (PARI) forstep( k=1,250,2, isprime(2*k+1) && print1(k", ")) \\ _M. F. Hasler_, Feb 25 2011

%o (PARI) forprime( p=1,500, p%4==3 || next; print1(p\2", ")) \\ _M. F. Hasler_, Feb 25 2011

%o (Magma) [n: n in [1..500 by 2] | IsPrime(2*n+1)]; // _Vincenzo Librandi_, Aug 14 2018

%Y Cf. A002145, A005097, A104636.

%K easy,nonn

%O 1,2

%A _Zak Seidov_, Mar 18 2005