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 A299975 #4 Feb 23 2018 09:48:35
%S A299975 1,4,11,14,21,24,26,9,6,19,16,29,22,3,2,13,12,23,27,8,7,18,17,28,25,
%T A299975 10,5,20,15,30,35,40,45,50,55,60,65,70,75,76,39,36,49,46,59,56,69,66,
%U A299975 79,71,34,31,44,41,54,51,64,61,74,77,38,37,48,47,58,57,68,67,78,72,33,32,43,42,53,52,63,62,73,80,85,90,95,100,105,110,115,120,125
%N A299975 Lexicographic first sequence of positive integers such that a(n) + a(n+1) has a digit 5, and no term occurs twice.
%C A299975 A permutation of the positive integers.
%o A299975 (PARI) a(n,f=1,d=5,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 A299975 Cf. A299985 (analog with nonnegative terms), A299957 (analog with digit 1), A299971, A299972, ..., A299979 (digit 0, 2, ..., 9).
%K A299975 nonn,base
%O A299975 1,2
%A A299975 _M. F. Hasler_ and _Eric Angelini_, Feb 22 2018