login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A100556 Composite numbers q such that 2^q + q is prime. 0

%I #19 May 01 2023 10:01:51

%S 9,15,39,75,81,735,1311,1881,3201,3225,11795,88071,204129,678561

%N Composite numbers q such that 2^q + q is prime.

%H Cino Hilliard, <a href="http://groups.msn.com/BC2LCC/2qqisprime3divq.msnw">Title?</a>. [Dead link]

%e For q = 9, 2^9 + 9 = 521, prime.

%e Note that 2^11795 + 11795 is prime but 11795 is composite and not divisible by 3.

%t Do[If[ !PrimeQ[n] && PrimeQ[2^n + n], Print[n]], {n, 2, 10^6}] (* _Ryan Propper_, Jul 21 2006 *)

%t nn=15000;Select[Complement[Range[2,nn],Prime[Range[PrimePi[nn]]]], PrimeQ[2^#+#]&] (* _Harvey P. Dale_, May 05 2011 *)

%o (PARI) \ p^q + q is prime q not prime ptoqpq(p,n)= { local(x,y,q); for(q=6,n, if(q%2, if(!isprime(q), y=p^q+q; if(ispseudoprime(y),print(q","y",")) ) ) ) }

%Y Composite terms in A052007.

%K nonn,more

%O 1,1

%A _Cino Hilliard_, Jan 12 2005

%E a(11) from _Ryan Propper_, Jul 21 2006

%E a(12)-a(14) (using A052007) from _Michael S. Branicky_, Apr 30 2023

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 28 16:12 EDT 2024. Contains 371254 sequences. (Running on oeis4.)