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 A277972 #10 Dec 20 2021 05:28:26
%S A277972 1,2,3,8,5,4,14,15,24,10,12,13,16,6,7,17,26,18,9,11,19,20,21,22,23,25,
%T A277972 27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,
%U A277972 50,51,52,53,54,55,56,57,58,59,64,60,61,62,63,65,66,67,68,69
%N A277972 a(1) = 1. a(n) is the smallest unlisted number, the name of which contains the first letter of the name of a(n-1) in English.
%t A277972 name[n_]:=IntegerName[n,"Words"];a[1]=1;
%t A277972 a[n_]:=a[n]=Module[{i=1}, While[Or[MemberQ[Table[a[k],{k,1,n-1}],i],
%t A277972 !StringContainsQ[name[i],StringTake[name[a[n-1]],1]]],i++ ];i];
%t A277972 a/@Range[69] (* _Ivan N. Ianakiev_, Dec 20 2021 *)
%Y A277972 Cf. A277971.
%K A277972 easy,nonn,word
%O A277972 1,2
%A A277972 _Ivan N. Ianakiev_, Nov 07 2016