A204322 Numbers k such that 4*5^k + 1 is prime.

0, 2, 6, 18, 50, 290, 2582, 20462, 23870, 26342, 31938, 38122, 65034, 70130, 245538, 851878, 1052422, 1496566, 5380542, 8431178

Offset

1,2

Comments

All terms correspond to verified primes, that is, not merely probable primes. - Robert Price, Jan 16 2015

a(16) > 3*10^5. - Robert Price, Jan 16 2015

Links

Table of n, a(n) for n=1..20.

Mathematica

Select[Range[0, 2000], PrimeQ[4*5^#+1]&]

Prog

(PARI) is(n)=ispseudoprime(4*5^n+1) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

Sequence in context: A002900 A309087 A199770 * A196593 A248735 A219136

Adjacent sequences: A204319 A204320 A204321 * A204323 A204324 A204325

Keyword

nonn,more

Author

José María Grau Ribas, Jan 14 2012

Extensions

a(8)-a(15) from Robert Price, Jan 16 2015

a(16)-a(19) from Ryan Propper, Dec 20 2023

a(20) from Ryan Propper, Jan 04 2024

Status

approved