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 A222213 #17 Mar 31 2017 00:31:30
%S A222213 4,1,2,3,0,5,6,7,8,9,14,11,12,13,10,15,16,17,18,19,24,21,22,23,20,25,
%T A222213 26,27,28,29,34,31,32,33,30,35,36,37,38,39,4,1,2,3,0,5,6,7,8,9,54,51,
%U A222213 52,53,50,55,56,57,58,59,64,61,62,63,60,65,66,67,68,69,74,71,72,73,70,75
%N A222213 Replace all (decimal) digits '0' with '4' and vice versa.
%C A222213 The map which is applied to primes in A171019.
%H A222213 Vincenzo Librandi, <a href="/A222213/b222213.txt">Table of n, a(n) for n = 0..1000</a>
%t A222213 Table[FromDigits[IntegerDigits[n]/.{0->z,4->f}/.{z->4,f->0}],{n,0,80}] (* _Harvey P. Dale_, Feb 25 2013 *)
%o A222213 (PARI) A222213(n,d=[4,1,2,3,0,5,6,7,8,9])=sum(i=1,#n=digits(n),d[n[i]+1]*10^(#n-i),!n*d[1]) \\ N.B.: PARI's digits() function returns [] for 0.
%Y A222213 Cf. A222210-A222254.
%K A222213 nonn,base,easy
%O A222213 0,1
%A A222213 _M. F. Hasler_, Feb 12 2013