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 A135681 #7 Oct 26 2016 11:31:19
%S A135681 1,2,3,4,5,4,7,4,1,4,11,4,13,4,1,4,17,4,19,4,1,4,23,4,1,4,1,4,29,4,31,
%T A135681 4,1,4,1,4,37,4,1,4,41,4,43,4,1,4,47,4,1,4,1,4,53,4,1,4,1,4,59,4,61,4,
%U A135681 1,4,1,4,67,4,1,4,71,4,73
%N A135681 a(n)=n if n=1 or if n=prime. Otherwise, n=4 if n is even and n=1 if n is odd.
%H A135681 G. C. Greubel, <a href="/A135681/b135681.txt">Table of n, a(n) for n = 1..1000</a>
%t A135681 a[n_] := If[PrimeQ[n] || n == 1, n, If[EvenQ[n], 4, 1] ]; Table[a[n], {n,1,25}] (* _G. C. Greubel_, Oct 26 2016 *)
%Y A135681 Cf. A135679; A135580; A014681; A014682; A014683; A014684; A014685; A014686; A014687; A014688; A014689; A014690.
%K A135681 nonn
%O A135681 1,2
%A A135681 _Mohammad K. Azarian_, Dec 01 2007