A252733 - OEIS

%I #19 Apr 25 2016 11:50:04

%S 2,1,1,1,4,2,1,2,1,1,3,5,8,4,2,1,7,5,10,5,6,3,19,71,46,23,14,7,4,2,1,

%T 3,15,13,38,19,10,5,28,14,7,8,4,2,1,11,14,7,6,3,8,4,2,1,3,54,27,17,11,

%U 16,8,4,2,1,38,19,52,26,13,15,11

%N Smallest number k such that (k^2)*2^(2*n+1)-1 is a prime number.

%C If k=1 then 2*n+1 is a Mersenne exponent.

%H Pierre CAMI, <a href="/A252733/b252733.txt">Table of n, a(n) for n = 0..2500</a>

%e 2*2^1-1=3 prime so a(0)=2.

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

%e 1*2^5-1=31 prime so a(2)=1.

%t Table[k=1; While[Not[PrimeQ[k^2*2^(2*n+1)-1]],k++]; k,{n,0,100}] (* _Vaclav Kotesovec_, Dec 21 2014 *)

%o (PFGW & SCRIPT)

%o SCRIPT

%o DIM n,0

%o DIM k

%o OPENFILEOUT myf,a(n).txt

%o LABEL loop1

%o SET n,n+1

%o SET k,0

%o LABEL loop2

%o SET k,k+1

%o PRP k^2*2^(2*n+1)-1

%o IF ISPRP THEN GOTO a

%o GOTO loop2

%o LABEL a

%o WRITE myf,k

%o GOTO loop1

%K nonn

%O 0,1

%A _Pierre CAMI_, Dec 21 2014