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URL: https://oeis.org/A059610

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A059610
Numbers k such that 2^k - 9 is prime.
20
4, 5, 9, 11, 17, 21, 33, 125, 141, 243, 251, 285, 321, 537, 563, 699, 729, 2841, 3365, 8451, 8577, 9699, 9725, 21011, 22689, 33921, 51761, 655845, 676761, 3480081
OFFSET
1,1
COMMENTS
Except the first term 4, all terms are odd since 2^(2*m) - 9 = (2^m - 3)*(2^m + 3) is not prime for m > 2.
LINKS
Keith Conrad, Square patterns and infinitude of primes, University of Connecticut, 2019.
Henri Lifchitz and Renaud Lifchitz (Editors), Search for 2^n-9, PRP Top Records.
EXAMPLE
243 is in the sequence because 2^243 - 9 is prime.
MATHEMATICA
Select[Range[3, 20000], PrimeQ[2^#-9]&] (* Vladimir Joseph Stephan Orlovsky, Feb 26 2011 *)
PROG
(PARI) is(n)=isprime(2^n-9) \\ Charles R Greathouse IV, Feb 17 2017
CROSSREFS
Cf. Sequences of numbers k such that 2^k - d is prime: A000043 (d=1), A050414 (d=3), A059608 (d=5), A059609 (d=7), this sequence (d=9), A096817 (d=11), A096818 (d=13), A059612 (d=15), A059611 (d=17), A096819 (d=19), A096820 (d=21), A057220 (d=23), A356826 (d=29).
Sequence in context: A193584 A155149 A024821 * A341783 A319606 A230239
KEYWORD
nonn,more
AUTHOR
Andrey V. Kulsha, Feb 02 2001
EXTENSIONS
a(24)-a(25) from Max Alekseyev, a(26)-a(27) from Paul Underwood, added by Max Alekseyev, Feb 09 2012
a(28)-a(29) from Robert Price, Jan 25 2017
a(30) found by Stefano Morozzi, added by Elmo R. Oliveira, Nov 17 2023
STATUS
approved