A121765 Numbers n such that 6*n-1 is composite while 6*n+1 is prime.

6, 11, 13, 16, 21, 26, 27, 35, 37, 46, 51, 55, 56, 61, 62, 63, 66, 68, 73, 76, 81, 83, 90, 91, 96, 101, 102, 105, 112, 115, 118, 121, 122, 123, 125, 126, 128, 131, 142, 146, 151, 153, 156, 161, 165, 166, 168, 173, 178, 181, 186, 187, 188, 195, 200, 202, 206, 208, 216

Offset: 1

Author

Lekraj Beedassy, Aug 20 2006

Keywords

• nonn

Comments

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

Links

• G. C. Greubel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A121764.

Programs

GAP

Filtered([1..250], k-> not IsPrime(6*k-1) and IsPrime(6*k+1)); # G. C. Greubel, Feb 20 2019

Magma

[n: n in [1..250] | not IsPrime(6*n-1) and  IsPrime(6*n+1)]; // G. C. Greubel, Feb 20 2019

Mathematica

Select[Range[250], ! PrimeQ[6# - 1] && PrimeQ[6# + 1] &] (* Ray Chandler, Aug 22 2006 *)

PARI

for(n=1, 250, if(!isprime(6*n-1) && isprime(6*n+1), print1(n", "))) \\ G. C. Greubel, Feb 20 2019

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

Extensions

Extended by Ray Chandler, Aug 22 2006