This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A227180 #16 Dec 22 2016 00:35:37
%S A227180 4,6,8,9,10,12,14,16,18,20,22,24,26,27,30,32,34,36,38,40,42,44,46,48,
%T A227180 50,54,56,58,60,62,64,68,72,74,78,80,81,82,84,86,88,90,92,94,96,98,
%U A227180 100,102,104,106,108,110,114,116,118,120,122,126,128,132,134,136,138,140,142,144,146,150,152,156,158,160,162,164,166,168,170
%N A227180 Composite numbers n such that b^(n-1) == 1 (mod n) implies b == -1 or +1 (mod n).
%C A227180 The sequence is the union of A111305 with {3^k | k > 1}.
%C A227180 The composite numbers not in this sequence are the Fermat pseudoprimes A181780.
%t A227180 FQ[k_]:= Block[{},GCD[EulerPhi[k],k-1]==1||IntegerQ[Log[3,k]]];Select[Range[4,170],FQ]
%o A227180 (PARI) is(n)=for(b=2, n-2, if(Mod(b, n)^(n-1)==1, return(0))); !isprime(n) \\ _Charles R Greathouse IV_, Dec 22 2016
%Y A227180 Cf. A111305, A181780, A209211.
%K A227180 nonn
%O A227180 1,1
%A A227180 _Emmanuel Vantieghem_, Jul 03 2013