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A273009
Numbers k such that (2^k + 5) / 3 is prime.
0
0, 2, 4, 6, 12, 18, 24, 42, 84, 300, 390, 780, 822, 2430, 5508, 5514, 6492, 12372, 22680, 25770, 169416, 174240, 383544, 1007838, 1572882
OFFSET
1,2
COMMENTS
Larger members of the sequence generate probable primes only.
Corresponding prime numbers are: 2, 3, 7, 23, 1367, 87383, 5592407, 1466015503703,6447604371278022265099607,.. etc.
LINKS
Henri & Renaud Lifchitz, (2^n+5)/3 PRPs [PRP Top Records]
FORMULA
a(n) = 2*A261539(n).
MATHEMATICA
Select[Range[0, 10000], PrimeQ[(2^# + 5)/3] &]
PROG
(Magma) [n: n in [0..2000] | (2^n+5) mod 3 eq 0 and IsPrime((2^n+5) div 3)];
(PARI) is(n)=ispseudoprime((2^n+5)/3) \\ Charles R Greathouse IV, Jun 07 2016
CROSSREFS
Cf. A261539.
Sequence in context: A060735 A181416 A225566 * A051683 A215821 A332284
KEYWORD
nonn,more,hard
AUTHOR
Vincenzo Librandi, May 13 2016
STATUS
approved