A002732 Numbers k such that (4*k^2 + 1)/5 is prime.

4, 6, 11, 14, 21, 24, 26, 29, 31, 39, 44, 46, 51, 54, 76, 79, 89, 94, 99, 101, 111, 119, 124, 129, 131, 136, 146, 149, 154, 156, 164, 176, 179, 181, 194, 201, 211, 214, 229, 231, 239, 244, 246, 254, 261, 279, 286, 294, 301, 311, 314, 319, 326, 331, 346, 349

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• easy

References

• L. Euler, De numeris primis valde magnis (E283), reprinted in: Opera Omnia. Teubner, Leipzig, 1911, Series (1), Vol. 3, p. 24.
• N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000
• L. Euler, De numeris primis valde magnis (E283), The Euler Archive.

Programs

Magma

[n: n in [4..410] | IsPrime((4*n^2+1) div 5)]; // Vincenzo Librandi, Sep 25 2012

Mathematica

Select[Range[0, 400], PrimeQ[(4 #^2 + 1)/5] &] (* Vincenzo Librandi, Sep 25 2012 *)

PARI

is(n)=isprime((4*n^2+1)/5) \\ Charles R Greathouse IV, May 22 2017