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A102634 Numbers k such that 2^k + 13 is prime. 20
2, 4, 8, 20, 38, 64, 80, 292, 1132, 4108, 19934, 125278, 175628, 282184 (list; graph; refs; listen; history; text; internal format)
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
Cf. A019434 (2^k+1), A057732 (2^k+3), A059242 (2^k+5), A057195 (2^k+7), A057196 (2^k+9), A102633 (2^k+11), A102634 (this), A057197 (2^k+15), A057200 (2^k+17), A057221 (2^k+19), A057201 (2^k+21), A057203 (2^k+23).
Sequence in context: A296606 A222562 A252891 * A026520 A282983 A282953
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

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Last modified February 21 09:29 EST 2024. Contains 370228 sequences. (Running on oeis4.)