login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 56th year, we are closing in on 350,000 sequences, and we’ve crossed 9,700 citations (which often say “discovered thanks to the OEIS”).

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A303090 Numbers k such that 5^k + 2*k is a prime. 1
1, 2, 3, 7, 18, 27, 61, 721, 873, 2492, 8713 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

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

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 A343358 A002864

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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 30 22:31 EST 2021. Contains 349426 sequences. (Running on oeis4.)