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A006553 Numbers n such that n*3^n - 1 is prime.
(Formerly M1575)
14
1, 2, 6, 10, 18, 40, 46, 86, 118, 170, 1172, 1698, 1810, 2268, 4338, 18362, 72662, 88392, 94110, 161538, 168660, 292340, 401208, 560750, 1035092 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

REFERENCES

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

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

Steven Harvey, Generalized Woodall Search

MATHEMATICA

Select[Range[10000], PrimeQ[# 3^# - 1] &] (* Vincenzo Librandi, Dec 02 2015 *)

PROG

(MAGMA) [n: n in [0..1420] | IsPrime(n*3^n-1)]; // Vincenzo Librandi, Dec 02 2015

(PARI) is(n)=ispseudoprime(n*3^n-1) \\ Charles R Greathouse IV, Feb 20 2017

CROSSREFS

Sequence in context: A095357 A095358 A084481 * A054273 A127567 A169643

Adjacent sequences:  A006550 A006551 A006552 * A006554 A006555 A006556

KEYWORD

hard,nonn

AUTHOR

N. J. A. Sloane.

EXTENSIONS

More terms from Jud McCranie

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 05 2008

a(24)-a(25) from Harvey link by Ray Chandler, Apr 10 2016

STATUS

approved

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Last modified November 17 12:39 EST 2018. Contains 317276 sequences. (Running on oeis4.)