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 A222242 #13 Mar 31 2017 00:16:36
%S A222242 0,1,2,3,7,5,6,4,8,9,10,11,12,13,17,15,16,14,18,19,20,21,22,23,27,25,
%T A222242 26,24,28,29,30,31,32,33,37,35,36,34,38,39,70,71,72,73,77,75,76,74,78,
%U A222242 79,50,51,52,53,57,55,56,54,58,59,60,61,62,63,67,65,66,64,68,69,40,41,42,43,47,45
%N A222242 In the number n, replace all (decimal) digits '4' with '7' and vice versa.
%C A222242 The map which is applied to primes in A171038.
%H A222242 Vincenzo Librandi, <a href="/A222242/b222242.txt">Table of n, a(n) for n = 0..1000</a>
%t A222242 Table[FromDigits[IntegerDigits[n]/.{4->a,7->b}/.{a->7,b->4}],{n,0,80}] (* _Harvey P. Dale_, Jul 22 2013 *)
%o A222242 (PARI) A222242(n,d=[0, 1, 2, 3, 7, 5, 6, 4, 8, 9])={sum(i=1,#n=digits(n),d[n[i]+1]*10^(#n-i),!n*d[1])} \\ N.B.: digits(0)=[] in PARI (v.2.6)
%Y A222242 Cf. A222210-A222254; A171013-A171016, A175770, A171018-A171057.
%K A222242 nonn,base,easy
%O A222242 0,3
%A A222242 _M. F. Hasler_, Feb 13 2013