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A259826 Numbers n such that n is a multiple of 6 and both n-1 and n+1 are composite. 2


%S 120,144,186,204,216,246,288,300,324,342,414,426,474,516,528,534,552,

%T 582,624,636,666,696,714,780,792,804,816,834,846,870,894,900,924,960,

%U 1002,1026,1044,1056,1074,1080,1134,1140,1146,1158,1176,1206,1242,1254,1266,1272,1314,1332,1338,1344,1350

%N Numbers n such that n is a multiple of 6 and both n-1 and n+1 are composite.

%H Harvey P. Dale, <a href="/A259826/b259826.txt">Table of n, a(n) for n = 1..2500</a>

%e For n=120, 120 is a multiple of 6, and both 119 and 121 are composite.

%t Select[6*Range[500], AllTrue[# + {1, -1}, CompositeQ] &] (* _Harvey P. Dale_, May 21 2017 *)

%o (PARI) select(x->!isprime(x-1)&&!isprime(x+1), vector(10^3,j,6*j) ) \\ _Joerg Arndt_, Jul 06 2015

%o (MAGMA) [n: n in [6..2000 by 6] | not IsPrime(n-1) and not IsPrime(n+1)]; // _Vincenzo Librandi_, Jul 08 2015

%Y Intersection of A008588 and A099047. - _Michel Marcus_, Jul 06 2015

%Y Cf. A060461.

%K nonn

%O 1,1

%A _Antonio Gimenez_, Jul 05 2015

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Last modified December 16 06:18 EST 2019. Contains 330016 sequences. (Running on oeis4.)