A121765 - OEIS

%I #15 Sep 08 2022 08:45:27

%S 6,11,13,16,21,26,27,35,37,46,51,55,56,61,62,63,66,68,73,76,81,83,90,

%T 91,96,101,102,105,112,115,118,121,122,123,125,126,128,131,142,146,

%U 151,153,156,161,165,166,168,173,178,181,186,187,188,195,200,202,206,208,216

%N Numbers n such that 6*n-1 is composite while 6*n+1 is prime.

%C Entries in A046953 which are not in A060461 or equivalently, entries in A024899 which are not in A002822.

%H G. C. Greubel, <a href="/A121765/b121765.txt">Table of n, a(n) for n = 1..10000</a>

%t Select[Range[250], ! PrimeQ[6# - 1] && PrimeQ[6# + 1] &] (* _Ray Chandler_, Aug 22 2006 *)

%o (PARI) for(n=1, 250, if(!isprime(6*n-1) && isprime(6*n+1), print1(n", "))) \\ _G. C. Greubel_, Feb 20 2019

%o (Magma) [n: n in [1..250] | not IsPrime(6*n-1) and  IsPrime(6*n+1)]; // _G. C. Greubel_, Feb 20 2019

%o (Sage)[n for n in (1..250) if not is_prime(6*n-1) and  is_prime(6*n+1)] # _G. C. Greubel_, Feb 20 2019

%o (GAP) Filtered([1..250], k-> not IsPrime(6*k-1) and IsPrime(6*k+1)) # _G. C. Greubel_, Feb 20 2019

%Y Cf. A121764.

%K nonn

%O 1,1

%A _Lekraj Beedassy_, Aug 20 2006

%E Extended by _Ray Chandler_, Aug 22 2006