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 A222221 #11 Mar 31 2017 00:26:19
%S A222221 0,4,2,3,1,5,6,7,8,9,40,44,42,43,41,45,46,47,48,49,20,24,22,23,21,25,
%T A222221 26,27,28,29,30,34,32,33,31,35,36,37,38,39,10,14,12,13,11,15,16,17,18,
%U A222221 19,50,54,52,53,51,55,56,57,58,59,60,64,62,63,61,65,66,67,68,69,70,74,72,73,71,75
%N A222221 In the number n, replace all (decimal) digits '1' with '4' and vice versa.
%C A222221 The map which is applied to primes in A171020.
%H A222221 Vincenzo Librandi, <a href="/A222221/b222221.txt">Table of n, a(n) for n = 0..1000</a>
%t A222221 a[n_]:= IntegerDigits[n]/.{1->4, 4->1} // FromDigits; Table[a[n], {n, 0, 80}] (* _Vincenzo Librandi_, Jul 29 2013 *)
%o A222221 (PARI) A222221(n,d=[0,4,2,3,1,5,6,7,8,9])=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 A222221 Cf. A222210-A222254; A171013-A171016, A175770, A171018-A171057.
%K A222221 nonn,base,easy
%O A222221 0,2
%A A222221 _M. F. Hasler_, Feb 12 2013