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

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

Offset: 1

Author

Zak Seidov, Mar 18 2005

Keywords

• easy
• nonn

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

Crossrefs

Cf. A002145, A005097, A104636.

Programs

Magma

[n: n in [1..500 by 2] | IsPrime(2*n+1)]; // Vincenzo Librandi, Aug 14 2018

Mathematica

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

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

Formula

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