A217349 - OEIS

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A217349

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

1, 2, 3, 4, 5, 8, 9, 10, 14, 15, 19, 22, 39, 44, 49, 63, 80, 87, 102, 107, 294, 305, 399, 463, 595, 599, 903, 944, 1324, 1727, 1755, 1932, 1935, 4485, 6165, 6665, 9438, 11169, 19859, 27503, 55392, 86235, 98217, 117855, 123640, 134204, 139660, 150437, 157634, 186475, 236129, 283248, 390142, 410178

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OFFSET

1,2

COMMENTS

The next terms are > 4.1*10^5. - Elmo R. Oliveira, Nov 29 2023

LINKS

Table of n, a(n) for n=1..54.

FORMULA

a(n) = A057195(n)/2.

EXAMPLE

For k = 14, 4^14 + 7 = 268435463 is prime.

MATHEMATICA

Select[Range[0, 5000], PrimeQ[4^# + 7] &]

PROG

(PARI) is(n)=ispseudoprime(4^n+7) \\ Charles R Greathouse IV, Jun 06 2017

CROSSREFS

Cf. A057195, A059266, A089437, A104066 (associated primes).

Sequence in context: A243490 A094566 A190018 * A329574 A087278 A054220

Adjacent sequences: A217346 A217347 A217348 * A217350 A217351 A217352

KEYWORD

nonn

AUTHOR

Vincenzo Librandi, Oct 01 2012

EXTENSIONS

Extended using A057195 terms by Michel Marcus, Aug 28 2015

a(51)-a(54) derived from A057195 by Elmo R. Oliveira, Nov 29 2023

STATUS

approved