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 A107130 #15 Apr 07 2022 23:44:29
%S A107130 0,0,2,1,4,2,6,3,8,4,0,0,2,1,4,2,6,3,8,4,20,20,22,21,24,22,26,23,28,
%T A107130 24,10,10,12,11,14,12,16,13,18,14,40,40,42,41,44,42,46,43,48,44,20,20,
%U A107130 22,21,24,22,26,23,28,24,60,60,62,61,64,62,66,63,68,64,30,30,32,31,34,32
%N A107130 Replace each odd digit d of n with (d-1)/2.
%C A107130 Differs from A065423 starting with a(10) = 0, A065423(10) = 10.
%H A107130 Vincenzo Librandi, <a href="/A107130/b107130.txt">Table of n, a(n) for n = 0..5000</a>
%t A107130 a[n_]:=FromDigits[Map[If[Mod[ #, 2]==1, (#-1)/2, # ]&, IntegerDigits[n]]];Table[a[n], {n, 0, 100}]
%o A107130 (Python)
%o A107130 def A107130(n): return int(str(n).translate({49:48,51:49,53:50,55:51,57:52})) # _Chai Wah Wu_, Apr 07 2022
%o A107130 (PARI) a(n)=fromdigits(apply(d->if(d%2,d\2,d),digits(n))) \\ _Charles R Greathouse IV_, Apr 07 2022
%Y A107130 Cf. A065423.
%K A107130 nonn,base,easy
%O A107130 0,3
%A A107130 _Zak Seidov_, May 12 2005
%E A107130 Edited by _Charles R Greathouse IV_, Aug 03 2010