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A273009 Numbers n such that (2^n + 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 (list; graph; refs; listen; history; text; internal format)
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

Table of n, a(n) for n=1..25.

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 A192096

Adjacent sequences:  A273006 A273007 A273008 * A273010 A273011 A273012

KEYWORD

nonn,more

AUTHOR

Vincenzo Librandi, May 13 2016

STATUS

approved

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Last modified June 19 00:55 EDT 2019. Contains 324217 sequences. (Running on oeis4.)