%I #10 Sep 08 2022 08:45:15

%S 3,5,7,8,9,10,11,13,14,15,16,17,19,20,21,22,23,24,25,26,27,28,29,31,

%T 32,33,34,35,36,37,38,39,40,41,43,44,45,46,47,48,49,50,51,52,53,54,55,

%U 56,57,58,59,61,62,63,64,65,66,67,68,69,70,71,73,74,75,76,77,78,79,80,81

%N Numbers n such that at least one of n-1 and n+1 is composite.

%C All odd numbers > 1 occur in this sequence. For the subsequence of even terms, see A100319.

%H G. C. Greubel, <a href="/A100318/b100318.txt">Table of n, a(n) for n = 1..10000</a>

%t Select[Range[3, 100], CompositeQ[#-1] || CompositeQ[#+1] &] (* _G. C. Greubel_, Apr 25 2019 *)

%o (PARI) for(n=3,100,if(isprime(n-1)+isprime(n+1)<=1,print1(n,",")))

%o (Magma) [n: n in [3..100] | not IsPrime(n-1) or not IsPrime(n+1) ]; // _G. C. Greubel_, Apr 25 2019

%o (Sage) [n for n in (3..100) if (is_prime(n-1) + is_prime(n+1) <= 1)] # _G. C. Greubel_, Apr 24 2019

%Y Cf. A100317 (exactly one of n-1 and n+1 is prime/composite), A100319.

%K nonn

%O 1,1

%A _Rick L. Shepherd_, Nov 13 2004