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 A135684 #9 Sep 08 2022 08:45:32
%S A135684 1,11,11,4,11,6,11,8,9,10,11,12,11,14,15,16,11,18,11,20,21,22,11,24,
%T A135684 25,26,27,28,11,30,11,32,33,34,35,36,11,38,39,40,11,42,11,44,45,46,11,
%U A135684 48,49,50,51,52,11,54,55,56,57,58,11
%N A135684 a(n)=11 if n is a prime number. Otherwise, a(n)=n.
%H A135684 Vincenzo Librandi, <a href="/A135684/b135684.txt">Table of n, a(n) for n = 1..1000</a>
%t A135684 Table[If[PrimeQ[n], 11, n], {n, 70}] (* _Vincenzo Librandi_, Feb 22 2013 *)
%o A135684 (Magma) [IsPrime(n) select 11 else n: n in [1..70]]; // _Vincenzo Librandi_, Feb 22 2013
%Y A135684 Cf. A000027; A000040; A135679; A135680; A014681; A014682; A014683; A014684; A014685; A014686; A014687; A014688; A014689; A014690; A135681; A135682; A135683.
%K A135684 nonn,easy
%O A135684 1,2
%A A135684 _Mohammad K. Azarian_, Dec 01 2007