OFFSET
1,1
COMMENTS
If k is odd, then 2^k + 13 is divisible by 3. - Robert G. Wilson v, Jan 24 2005
a(15) > 5*10^5. - Robert Price, Aug 15 2015
For k in this sequence, the number 2^(k-1)*(2^k+13) has deficiency 14, cf. A141550. - M. F. Hasler, Jul 18 2016
LINKS
H. Lifchitz and R. Lifchitz (Editors), PRP Top Records, of the form 2^n+13.
Lei Zhou, Between 2^n and primes [broken link].
FORMULA
a(n) = 2*A253772(n). - Elmo R. Oliveira, Nov 12 2023
EXAMPLE
2^2+13 = 17 is prime.
2^4+13 = 29 is prime.
2^3+13 = 21 is not prime.
MATHEMATICA
Do[m = n; If[PrimeQ[2^n + 13], Print[n]], {n, 2, 19125, 2}] (* Robert G. Wilson v, Jan 24 2005 *)
PROG
(PARI) first(m)=my(v=vector(m), r=1); for(i=1, m, while(!isprime(2^r + 13), r++); v[i]=r; r++); v; \\ Anders Hellström, Aug 15 2015
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Lei Zhou, Jan 20 2005
EXTENSIONS
a(10) from Robert G. Wilson v, Jan 24 2005
a(11)-a(14) from Robert Price, Aug 15 2015
STATUS
approved