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 A222228 #10 Mar 31 2017 00:23:41
%S A222228 0,1,4,3,2,5,6,7,8,9,10,11,14,13,12,15,16,17,18,19,40,41,44,43,42,45,
%T A222228 46,47,48,49,30,31,34,33,32,35,36,37,38,39,20,21,24,23,22,25,26,27,28,
%U A222228 29,50,51,54,53,52,55,56,57,58,59,60,61,64,63,62,65,66
%N A222228 In the number n, replace all (decimal) digits '2' with '4' and vice versa.
%C A222228 The map which is applied to primes in A171021.
%H A222228 Vincenzo Librandi, <a href="/A222228/b222228.txt">Table of n, a(n) for n = 0..1000</a>
%t A222228 a[n_]:= IntegerDigits[n]/.{2->4, 4->2} // FromDigits; Table[a[n], {n, 0, 80}] (* _Vincenzo Librandi_, Jul 30 2013 *)
%o A222228 (PARI) A222228(n,d=[0,1,4,3,2,5,6,7,8,9])=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)
%Y A222228 Cf. A222210-A222254; A171013-A171016, A175770, A171018-A171057.
%K A222228 nonn,base,easy
%O A222228 0,3
%A A222228 _M. F. Hasler_, Feb 12 2013