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 A247681 #27 Sep 02 2020 03:06:58
%S A247681 1,55,91,145,217,235,253,289,325,343,361,415,451,469,505,559,595,649,
%T A247681 667,685,703,721,775,793,847,865,901,955,973,1027,1045,1081,1099,1135,
%U A247681 1189,1207,1225,1243,1261,1315,1333,1351,1369,1387,1405
%N A247681 Odd nonprimes congruent to 1 modulo 9.
%C A247681 Subsequence of A017173.
%H A247681 Odimar Fabeny, <a href="/A247681/b247681.txt">Table of n, a(n) for n = 1..10000</a>
%t A247681 Select[18Range[0, 99] + 1, Not[PrimeQ[#]] &] (* _Alonso del Arte_, Sep 25 2014 *)
%t A247681 Select[Range[1,1500,18],!PrimeQ[#]&] (* _Harvey P. Dale_, Mar 07 2018 *)
%o A247681 (PARI) lista(nn) = {forcomposite(n=1, nn, if ((n % 2) && ((n % 9) == 1), print1(n, ", ")); ); } \\ _Michel Marcus_, Sep 22 2014
%Y A247681 Cf. A017173, A247676, A247678, A247679, A247682, A247683, A247900 (first differences).
%K A247681 nonn,easy
%O A247681 1,2
%A A247681 _Odimar Fabeny_, Sep 22 2014