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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A339921 Numbers k such that 20^k + 3 is prime. 1

%I

%S 1,5,7,13,15,18,22,61,85,208,271,898,2142,2856,4392,17171,74886,78901,

%T 271951,326600

%N Numbers k such that 20^k + 3 is prime.

%e 1 is a term since 20^1 + 3 = 23 is a prime.

%t Do[ If[ PrimeQ[ 20^n + 3], Print[n]], {n, 0, 100000}]

%o (PARI) is(n)=isprime(20^n + 3)

%Y Cf. A339922.

%K nonn,more

%O 1,2

%A _Paul Bourdelais_, Dec 23 2020

%E a(19)-a(20) correspond to probable primes discovered by _Paul Bourdelais_, Jan 06 2021

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 October 25 14:34 EDT 2021. Contains 348255 sequences. (Running on oeis4.)