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A195732
Numbers k such that 2*(3^k-k)-1 is prime.
1
1, 2, 3, 11, 30, 62, 534, 620, 803, 2436, 2669, 3975, 4530, 4827, 5294, 15987, 17589, 51960
OFFSET
1,2
COMMENTS
According to Maple version 14, the next entries are 534, 620 and 803, but these involve primes of 256 and more digits and may not be certified primes. - R. J. Mathar, Sep 23 2011
a(19) > 10^5, if it exists. - Michael S. Branicky, Aug 26 2024
EXAMPLE
1 is in the sequence because 2*3^1-2*1-1 = 3 is a prime.
2 is in the sequence because 2*3^2-2*2-1 = 13 is a prime.
3 is in the sequence because 2*3^3-2*3-1=47 ts a prime.
4 is not in the sequence because 2*3^4-2*4-1 = 153 = 3^2*17 is not prime.
PROG
(PARI) is(n)=ispseudoprime(2*(3^n-n)-1) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
Cf. A048473.
Sequence in context: A003455 A103275 A278209 * A038987 A142957 A191058
KEYWORD
nonn,more
AUTHOR
EXTENSIONS
a(10)-a(18) from Michael S. Branicky, Jul 14 2023
STATUS
approved