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 A174025 #16 May 22 2020 01:12:30 %S A174025 0,1,2,3,4,5,6,7,8,9,19,18,17,16,15,14,13,12,11,10,20,21,22,23,24,25, %T A174025 26,27,28,29,39,38,37,36,35,34,33,32,31,30,40,41,42,43,44,45,46,47,48, %U A174025 49,59,58,57,56,55,54,53,52,51,50,60,61,62,63,64,65,66,67,68,69,79,78,77 %N A174025 Inverse permutation to A003100. %H A174025 Franklin T. Adams-Watters, <a href="/A174025/b174025.txt">Table of n, a(n) for n = 0..10000</a> %H A174025 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a> %o A174025 (PARI) inbase(n,b)=local(r);r=[];while(n>0,r=concat([n%b],r);n\=b);r %o A174025 tobase(v,b)=local(r);for(i=1,#v,r=r*b+v[i]);r %o A174025 a(n)=local(v);v=inbase(n,10);for(k=2,#v,if(v[k-1]%2==1,v[k]=9-v[k]));tobase(v,10) %K A174025 base,easy,nonn %O A174025 0,3 %A A174025 _Franklin T. Adams-Watters_, Mar 05 2010