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A199716 Numbers n such that 6n-5 and 6n-1 are both composite. 0
16, 20, 21, 35, 37, 50, 51, 54, 55, 61, 66, 68, 76, 79, 81, 83, 86, 89, 90, 105, 112, 115, 118, 121, 125, 128, 130, 131, 134, 141, 142, 145, 146, 149, 150, 151, 153, 156, 160, 161, 165, 168, 180, 181, 186, 190, 191, 195, 200, 202, 208, 211, 212, 219, 223 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..55.

MATHEMATICA

Select[Range[223], ! PrimeQ[6#-5] && ! PrimeQ[6#-1] &] (* T. D. Noe, Nov 09 2011 *)

Select[Range[250], AllTrue[6#+{-5, -1}, CompositeQ]&] (* Requires Mathematica version 10 or later *)  (* Harvey P. Dale, Oct 11 2018 *)

PROG

(MAGMA) [ n: n in [1..223] | not IsPrime(6*n-5) and not IsPrime(6*n-1) ];  // Bruno Berselli, Nov 09 2011

(PARI) for(n=1, 1e3, if(!isprime(6*n-5)&&!isprime(6*n-1), print1(n", "))) \\ Charles R Greathouse IV, Nov 10 2011

CROSSREFS

Cf. A186243.

Sequence in context: A335210 A061934 A195683 * A163901 A044860 A272533

Adjacent sequences:  A199713 A199714 A199715 * A199717 A199718 A199719

KEYWORD

nonn,easy

AUTHOR

Eleonora Echeverri-Toro, Nov 09 2011

STATUS

approved

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Last modified June 25 06:20 EDT 2021. Contains 345452 sequences. (Running on oeis4.)