

A104635


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


6



1, 3, 5, 9, 11, 15, 21, 23, 29, 33, 35, 39, 41, 51, 53, 63, 65, 69, 75, 81, 83, 89, 95, 99, 105, 111, 113, 119, 125, 131, 135, 141, 153, 155, 165, 173, 179, 183, 189, 191, 209, 215, 219, 221, 231, 233, 239, 243, 245, 249, 251, 261, 273, 281, 285, 293, 299
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,2


COMMENTS

Also: Numbers k such that 2k+1 is in A002145, i.e., a Gaussian prime.  M. F. Hasler, Feb 25 2011
Also: Number of quadratic residues modulo A002145(n).  M. F. Hasler, Feb 25 2011


LINKS

G. C. Greubel, Table of n, a(n) for n = 1..10000


FORMULA

a(n) = floor(A002145(n)/2).  M. F. Hasler, Feb 25 2011


MATHEMATICA

Select[Range[1, 301, 2], PrimeQ[2#+1]&] (* Harvey P. Dale, May 08 2012 *)


PROG

(PARI) forstep( k=1, 250, 2, isprime(2*k+1) && print1(k", ")) \\ M. F. Hasler, Feb 25 2011
(PARI) forprime( p=1, 500, p%4==3  next; print1(p\2", ")) \\ M. F. Hasler, Feb 25 2011
(Magma) [n: n in [1..500 by 2]  IsPrime(2*n+1)]; // Vincenzo Librandi, Aug 14 2018


CROSSREFS

Cf. A002145, A005097, A104636.
Sequence in context: A161830 A151922 A233762 * A210537 A199407 A261141
Adjacent sequences: A104632 A104633 A104634 * A104636 A104637 A104638


KEYWORD

easy,nonn


AUTHOR

Zak Seidov, Mar 18 2005


STATUS

approved



