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 A035043 #21 Jun 01 2022 01:56:43
%S A035043 0,2,1,3,4,5,6,7,8,9,20,22,21,23,24,25,26,27,28,29,10,12,11,13,14,15,
%T A035043 16,17,18,19,30,32,31,33,34,35,36,37,38,39,40,42,41,43,44,45,46,47,48,
%U A035043 49,50,52,51,53,54,55,56,57,58,59,60,62,61,63,64,65,66,67,68
%N A035043 Replace any decimal digit '1' with '2' and vice versa.
%C A035043 The map which is applied to primes in A171015. - _M. F. Hasler_, Feb 12 2013
%H A035043 Vincenzo Librandi, <a href="/A035043/b035043.txt">Table of n, a(n) for n = 0..1000</a>
%t A035043 a[n_]:= IntegerDigits[n]/.{1->2, 2->1} // FromDigits; Table[a[n], {n, 0, 80}] (* _Vincenzo Librandi_, Jul 29 2013 *)
%o A035043 (PARI) A035043(n, d=[0, 2, 1, 3, 4, 5, 6, 7, 8, 9])=sum(i=1, #n=digits(n), d[n[i]+1]*10^(#n-i)) \\ gives correct value for n=0 iff d[1]=0, since digits(0)=[] in PARI (v.2.6) _M. F. Hasler_, Feb 12 2013
%Y A035043 Cf. A222210 - A222254; A171013 - A171016, A175770, A171018 - A171057.
%K A035043 nonn,base,easy
%O A035043 0,2
%A A035043 _N. J. A. Sloane_
%E A035043 Definition rephrased by _M. F. Hasler_, Oct 26 2013