A096305 Numbers k such that 7^k + 4 is prime.

0, 1, 2, 3, 5, 7, 9, 14, 23, 129, 198, 235, 275, 630, 870, 1033, 1290, 3293, 3458, 11466, 13885, 25893, 32186, 33139, 58125, 78929, 97197, 121933, 128422, 442674

Offset: 1

Author

Herman H. Rosenfeld (herm3(AT)pacbell.net), Jun 26 2004

Keywords

• nonn
• more

Examples

			7^14 + 4 = 678223072853 is a prime number.
		

Crossrefs

Cf. A236371, A217131, A191469, A090669, A096305, A217130, A217132, A152213.

Programs

Mathematica

Do[If[PrimeQ[7^n+4], Print[n]], {n, 1, 1000}]

PARI

for(n=0, 10^5, if(ispseudoprime(7^n+4), print1(n, ", "))) \\  Felix Fröhlich, Jun 04 2014

Extensions

More terms (probable primes) from Rick L. Shepherd, Jun 29 2004

7 more terms from Jason Earls, Feb 16 2008

a(25)-a(27) from Robert Price, Jan 24 2014

a(28)-a(29) from Lelio R. Paula, Nov 2014

a(30) from Paul Bourdelais, Feb 11 2021