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Numbers n such that 18n-1 is prime.
6

%I #29 Sep 08 2022 08:45:33

%S 1,3,4,5,6,10,11,13,14,15,20,24,25,26,28,29,31,33,36,38,39,40,43,45,

%T 46,48,49,53,54,59,61,64,66,68,70,71,76,80,83,84,88,89,90,91,95,104,

%U 105,106,110,111,115,116,119,123,126,130,131,133,134,136,144,145,148,150

%N Numbers n such that 18n-1 is prime.

%C Corresponding primes are in A061242.

%C No terms in this sequence end with 2 or 7 (18n-1 ends with 5 when the last digit of n is 2 or 7). - _David Garber_, Jun 25 2015

%H Zak Seidov, <a href="/A138918/b138918.txt">Table of n, a(n) for n = 1..1000</a>

%t Select[Range[200],PrimeQ[18#-1]&] (* _Harvey P. Dale_, Mar 09 2011 *)

%o (Python)

%o from gmpy2 import divexact, t_mod

%o from sympy import prime

%o A138918 = [divexact(p+1,18) for p in (prime(n) for n in range(1,10**6)) if not t_mod(p+1,18)] # _Chai Wah Wu_, Sep 02 2014

%o (PARI) for(n=1,10^3,if(isprime(18*n-1),print1(n,", "))) \\ _Derek Orr_, Sep 03 2014

%o (Magma) [n: n in [0..150] | IsPrime(18*n-1)]; // _Vincenzo Librandi_, Jun 27 2015

%Y Cf. A061242, A258663.

%K nonn,easy

%O 1,2

%A _Zak Seidov_, Apr 03 2008