A303090 Numbers k such that 5^k + 2*k is prime.

1, 2, 3, 7, 18, 27, 61, 721, 873, 2492, 8713

Offset

1,2

Comments

a(12) > 20000. - Jon E. Schoenfield, Apr 19 2018

a(12) > 40000. - Michael S. Branicky, Apr 13 2023

a(12) > 100000. - Michael S. Branicky, Nov 25 2024

Links

Table of n, a(n) for n=1..11.

Example

1 is a term because 5^1 + 2*1 = 5 + 2 = 7, a prime.
2 is a term because 5^2 + 2*2 = 25 + 4 = 29, a prime.
3 is a term because 5^3 + 2*3 = 125 + 6 = 131, a prime.

Maple

a:=k->`if`(isprime(5^k+2*k), k, NULL): seq(a(k), k=1..5500);

Prog

(GAP) Filtered([1..700], k->IsPrime(5^k+2*k));
(PARI) isok(k) = isprime(5^k + 2*k); \\ Altug Alkan, Apr 19 2018

Crossrefs

Cf. A299642, A299643, A297663.

Sequence in context: A295509 A225747 A058334 * A131093 A359089 A343358

Adjacent sequences: A303087 A303088 A303089 * A303091 A303092 A303093

Keyword

nonn,more

Author

Muniru A Asiru, Apr 18 2018

Extensions

a(11) from Jon E. Schoenfield, Apr 18 2018

Status

approved