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 A030155 #6 Aug 17 2018 10:48:05
%S A030155 1,3,5,7,9,11,13,19,23,27,31,69,81,111,113,119,127,137,181,187,237,
%T A030155 269,273,277,281,311,461,463,539,661,673,677,689,819,831,1019,1027,
%U A030155 1111,1113,1119,1127,1137,1269,1277,1287,1361,1369,1377,1863,1969
%N A030155 Odd n such that in n^2 the parity of digits alternates.
%H A030155 Giovanni Resta, <a href="/A030155/b030155.txt">Table of n, a(n) for n = 1..10000</a>
%t A030155 altQ[n_] := n < 10 || Union[Total /@ Partition[ Mod[ IntegerDigits@n, 2], 2, 1]] == {1}; Select[ Range[1, 2000, 2], altQ[#^2] &] (* _Giovanni Resta_, Aug 16 2018 *)
%Y A030155 Cf. A030151, A030152, A030156, A030157, A030158.
%K A030155 nonn,base
%O A030155 1,2
%A A030155 _Patrick De Geest_
%E A030155 Offset changed by _Giovanni Resta_, Aug 16 2018