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Numbers k such that k*3^k - 1 is prime.
(Formerly M1575)
14

%I M1575 #35 Sep 08 2022 08:44:35

%S 1,2,6,10,18,40,46,86,118,170,1172,1698,1810,2268,4338,18362,72662,

%T 88392,94110,161538,168660,292340,401208,560750,1035092

%N Numbers k such that k*3^k - 1 is prime.

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

%H Steven Harvey, <a href="http://harvey563.tripod.com/GeneralizedWoodallPrimes.txt">Generalized Woodall Search</a>

%t Select[Range[10000], PrimeQ[# 3^# - 1] &] (* _Vincenzo Librandi_, Dec 02 2015 *)

%o (Magma) [n: n in [0..1420] | IsPrime(n*3^n-1)]; // _Vincenzo Librandi_, Dec 02 2015

%o (PARI) is(n)=ispseudoprime(n*3^n-1) \\ _Charles R Greathouse IV_, Feb 20 2017

%K hard,nonn

%O 1,2

%A _N. J. A. Sloane_

%E More terms from _Jud McCranie_

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

%E a(24)-a(25) from Harvey link by _Ray Chandler_, Apr 10 2016