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!)
A252734 Smallest odd prime Q such that Q^2*2^prime(n)-1 is a prime number starting with n=2. 1

%I

%S 3,7,3,5,3,5,83,5,7,43,11,23,3,71,47,97,109,13,19,17,53,83,97,53,43,

%T 97,5,3,43,17,19,13,307,103,293,13,11,457,113,317,67,47,311,127,281,3,

%U 97,13,127,1223,61,307,29

%N Smallest odd prime Q such that Q^2*2^prime(n)-1 is a prime number starting with n=2.

%H Pierre CAMI, <a href="/A252734/b252734.txt">Table of n, a(n) for n = 2..1800</a>

%e 3^2*2^3-1=71 prime so a(2)=3.

%e 7^2*2^5-1=1567 prime so a(3)=7.

%t Table[k=3; While[Not[PrimeQ[k^2*2^Prime[n]-1]],k=NextPrime[k]]; k,{n,2,100}] (* _Vaclav Kotesovec_, Dec 21 2014 *)

%o (PFGW & SCRIPT)

%o SCRIPT

%o DIM n,1

%o DIM q

%o OPENFILEOUT myf,a(n).txt

%o LABEL loop1

%o SET n,n+1

%o SET q,1

%o LABEL loop2

%o SET q,q+1

%o PRP p(q)^2*2^p(n)-1

%o IF ISPRP THEN GOTO a

%o GOTO loop2

%o LABEL a

%o WRITE myf,q

%o GOTO loop1

%Y Cf. A252733.

%K nonn

%O 2,1

%A _Pierre CAMI_, Dec 21 2014

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 September 28 20:03 EDT 2021. Contains 347717 sequences. (Running on oeis4.)