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A104635 Odd n such that 2*n+1 is prime.

%I A104635 #23 Sep 08 2022 08:45:17
%S A104635 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 A104635 105,111,113,119,125,131,135,141,153,155,165,173,179,183,189,191,209,
%U A104635 215,219,221,231,233,239,243,245,249,251,261,273,281,285,293,299
%N A104635 Odd n such that 2*n+1 is prime.
%C A104635 Also: Numbers k such that 2k+1 is in A002145, i.e., a Gaussian prime. - _M. F. Hasler_, Feb 25 2011
%C A104635 Also: Number of quadratic residues modulo A002145(n). - _M. F. Hasler_, Feb 25 2011
%H A104635 G. C. Greubel, <a href="/A104635/b104635.txt">Table of n, a(n) for n = 1..10000</a>
%F A104635 a(n) = floor(A002145(n)/2). - _M. F. Hasler_, Feb 25 2011
%t A104635 Select[Range[1,301,2],PrimeQ[2#+1]&] (* _Harvey P. Dale_, May 08 2012 *)
%o A104635 (PARI) forstep( k=1,250,2, isprime(2*k+1) && print1(k", ")) \\ _M. F. Hasler_, Feb 25 2011
%o A104635 (PARI) forprime( p=1,500, p%4==3 || next; print1(p\2", ")) \\ _M. F. Hasler_, Feb 25 2011
%o A104635 (Magma) [n: n in [1..500 by 2] | IsPrime(2*n+1)]; // _Vincenzo Librandi_, Aug 14 2018
%Y A104635 Cf. A002145, A005097, A104636.
%K A104635 easy,nonn
%O A104635 1,2
%A A104635 _Zak Seidov_, Mar 18 2005