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 A030142 #20 Feb 14 2017 23:07:44
%S A030142 1,3,5,7,9,21,23,25,27,29,41,43,45,47,49,61,63,65,67,69,81,83,85,87,
%T A030142 89,101,103,105,107,109,121,123,125,127,129,141,143,145,147,149,161,
%U A030142 163,165,167,169,181,183,185,187,189,301,303,305,307,309,321,323
%N A030142 Odd numbers in which parity of digits alternates.
%C A030142 a(n) = A179085(n) for n <= 25. - _Reinhard Zumkeller_, Jun 28 2010
%H A030142 Reinhard Zumkeller, <a href="/A030142/b030142.txt">Table of n, a(n) for n = 1..10000</a>
%H A030142 <a href="/index/Ar#10-automatic">Index entries for 10-automatic sequences</a>.
%F A030142 (a(n) mod 2) * A228710(a(n)) = 1. - _Reinhard Zumkeller_, Aug 31 2013
%t A030142 id[n_]:=IntegerDigits[n];t={}; Do[If[Length[id[n]]==1, AppendTo[t,n], If[Union[Abs[Differences[Boole /@ EvenQ[id[n]]]]] == {1}, AppendTo[t,n]]], {n,1,323,2}]; t (* _Jayanta Basu_, May 07 2013 *)
%t A030142 Join[{1, 3, 5, 7, 9}, Select[Range[21, 323, 2], Total[Abs[Differences[Mod[(id = IntegerDigits[#]), 2]]]] == Length[id] - 1 &]] (* _Zak Seidov_, May 07 2013 *)
%o A030142 (Haskell)
%o A030142 a030142 n = a030142_list !! (n-1)
%o A030142 a030142_list = filter odd a030141_list
%o A030142 -- _Reinhard Zumkeller_, Aug 31 2013
%Y A030142 Cf. A030143, A062285, intersection of A005408 and A030141.
%K A030142 nonn,base,easy
%O A030142 1,2
%A A030142 _Patrick De Geest_
%E A030142 Offset corrected by _Reinhard Zumkeller_, Jun 28 2010