## x^r + a is prime

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• Hi, A twist on the old x^y - y^x prime search is x^r + a where r is the reverse of the digits of x and a is an integer. See Pari code below For example
Message 1 of 1 , Aug 22, 2009
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Hi,

A twist on the old x^y - y^x prime search is x^r + a where r is the reverse
of the digits of x and a is an integer. See Pari code below

For example

g(1000,2)
0,1,3,39,51,87,113,737,831,

737^737+2 is a 2114 digit prime

Version=3.0.7
WebSite=http://www.ellipsa.net/
ID=B31C802C933B8
Created=08/21/2009 12:59:00 PM

[Common]
Path=C:\primo\
Selected=1
Processed=1
Certified=1
Candidate #1=Certified, 18h 53mn 59s

[Candidate #1]
Input=737to737+2.in
Report=primo-B31C802C933B8-001.cr
Output=primo-B31C802C933B8-001.out
Status=Candidate certified prime

Pari code

g(n,a) = for(x=0,n,r=eval(rev(x));y=x^r+a;if(ispseudoprime(y),print1(x",")))

rev(str)=local(tmp,s,j);tmp=Vec(Str(str));s="";forstep(j=length(tmp),1,-1,

s=concat(s,tmp[j]));return(s)

Cino

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