A124198 - OEIS

%I #17 Sep 08 2022 08:45:28

%S 2,6,10,16,18,20,22,26,30,32,36,42,46,48,50,52,62,68,70,76,82,92,96,

%T 102,108,110,116,120,126,128,130,136,146,148,158,160,168,170,172,176,

%U 178,182,186,198,200,202,206,220,222,228,230,236,238,246,248,258,262,278

%N Numbers k such that 21*k + 1 is prime.

%H Harvey P. Dale, <a href="/A124198/b124198.txt">Table of n, a(n) for n = 1..1000</a>

%e If k=148 then 21*k + 1 = 3109 (prime).

%t Select[Range[300],PrimeQ[21#+1]&] (* _Harvey P. Dale_, Mar 08 2016 *)

%o (Magma) [n: n in [0..300] | IsPrime(21*n + 1)] // _Vincenzo Librandi_, Mar 26 2010

%o (PARI) is(n)=isprime(21*n+1) \\ _Charles R Greathouse IV_, Jun 06 2017

%Y Cf. A024905, A124127.

%K nonn,easy

%O 1,1

%A _Parthasarathy Nambi_, Dec 06 2006