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A100556 Composite numbers q such that 2^q + q is prime. 0
9, 15, 39, 75, 81, 735, 1311, 1881, 3201, 3225, 11795 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..11.

Cino Hilliard, Title?.

EXAMPLE

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

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

MATHEMATICA

Do[If[ !PrimeQ[n] && PrimeQ[2^n + n], Print[n]], {n, 2, 10^6}] (* Ryan Propper, Jul 21 2006 *)

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

PROG

(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", ")) ) ) ) }

CROSSREFS

Sequence in context: A133763 A146475 A307217 * A057478 A128687 A193579

Adjacent sequences:  A100553 A100554 A100555 * A100557 A100558 A100559

KEYWORD

more,nonn

AUTHOR

Cino Hilliard, Jan 12 2005

EXTENSIONS

One more term from Ryan Propper, Jul 21 2006

STATUS

approved

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Last modified May 31 00:06 EDT 2020. Contains 334747 sequences. (Running on oeis4.)