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A059610 Numbers n such that 2^n - 9 is prime. 16
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 (list; graph; refs; listen; history; text; internal format)
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

Table of n, a(n) for n=1..29.

Keith Conrad, Square patterns and infinitude of primes, University of Connecticut, 2019.

Henri Lifchitz & 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

Exponents for primes of the form 2^n - d: A000043 (d=1), A050414 (d=3), A059608 (d=5), A059609 (d=7), A059610 (d=9), A096817 (d=11), A096818 (d=13), A059612 (d=15), A059611 (d=17), A096819 (d=19), A096820 (d=21).

Sequence in context: A193584 A155149 A024821 * A230239 A194154 A297291

Adjacent sequences:  A059607 A059608 A059609 * A059611 A059612 A059613

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

STATUS

approved

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Last modified February 27 15:59 EST 2020. Contains 332307 sequences. (Running on oeis4.)