A100663 Composite q such that 4^q + q is prime.

9, 15, 85, 133, 225, 1233, 12793, 108889

Offset: 1

Author

Cino Hilliard, Jan 12 2005

Keywords

• nonn
• more

Crossrefs

Composites in A057909.

Programs

Mathematica

For[n = 1, n < 5000, n++, If[Not[PrimeQ[n]], If[PrimeQ[4^n + n], Print[n]]]] (Steinerberger)
Select[Range[2,10000],!PrimeQ[#]&&PrimeQ[4^#+#]&] (* Harvey P. Dale, Mar 09 2014 *)

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),print1(q",")) ) ) ) }

Extensions

a(6) from Stefan Steinerberger, Jan 27 2006

a(7)-a(8) using A057909 from Michael S. Branicky, Jun 28 2024