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 A299973 #6 Feb 23 2018 09:46:55
%S A299973 1,2,11,12,18,5,8,15,16,7,6,17,13,10,3,20,14,9,4,19,24,29,34,39,44,49,
%T A299973 54,59,64,66,27,26,37,36,47,46,57,56,67,63,30,23,40,33,50,43,60,53,70,
%U A299973 61,22
%N A299973 Lexicographic first sequence of positive integers such that a(n) + a(n+1) has a digit 3, and no term occurs twice.
%C A299973 A permutation of the positive integers.
%o A299973 (PARI) a(n,f=1,d=3,a=1,u=[a])={for(n=2,n,f&&if(f==1,print1(a","),write(f,n-1," "a));for(k=u[1]+1,oo,setsearch(u,k)&&next;setsearch(Set(digits(a+k)),d)&&(a=k)&&break);u=setunion(u,[a]);u[2]==u[1]+1&&u=u[^1]);a}
%Y A299973 Cf. A299983 (analog with nonnegative terms), A299957 (analog with digit 1), A299970..A299979 (digit 0..9).
%K A299973 nonn,base
%O A299973 1,2
%A A299973 _M. F. Hasler_ and _Eric Angelini_, Feb 22 2018