A094180 Numbers k such that 4*k-1 is divisible only by primes of form 4*m-1 (i.e., by the Gaussian primes A002145).

1, 2, 3, 5, 6, 7, 8, 11, 12, 15, 16, 17, 18, 20, 21, 25, 26, 27, 32, 33, 35, 37, 38, 41, 42, 43, 45, 48, 50, 52, 53, 56, 57, 58, 60, 61, 63, 66, 68, 70, 71, 77, 78, 83, 86, 87, 90, 91, 92, 95, 96, 97, 100, 105, 106, 108, 110, 111, 116, 117, 120, 121, 122, 123, 125, 126, 131

Offset: 1

Author

Lekraj Beedassy, May 06 2004

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

For the actual numbers 4*k-1, see A094179.

Cf. A002145.

Programs

Mathematica

Select[Range[150], AllTrue[FactorInteger[4*# - 1][[;; , 1]], Mod[#1, 4] == 3 &] &] (* Amiram Eldar, Apr 01 2021 *)

PARI

{for(n=1,140,fac=factor(4*n-1);v=vector(matsize(fac)[1],j,fac[j,1])%4;if(vecmin(v)==3,print1(n,",")))} \\ Klaus Brockhaus, May 08 2004

Formula

a(n) = (A094179(n) + 1)/4. - Amiram Eldar, Apr 01 2021

Extensions

More terms from Klaus Brockhaus, May 08 2004