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 A252481 #11 Jan 11 2021 01:45:38
%S A252481 1,10,11,12,21,100,101,102,110,111,112,120,121,122,123,132,201,210,
%T A252481 211,212,213,221,231,312,321,1000,1001,1002,1010,1011,1012,1020,1021,
%U A252481 1022,1023,1032,1100,1101,1102,1110,1111,1112,1120,1121,1122,1123,1132,1200,1201,1202,1203,1210,1211,1212,1213,1220,1221,1222,1223
%N A252481 Numbers whose set of digits is simply connected to 1.
%C A252481 "Simply connected" means that there must not be a "hole" in the set of digits. E.g., {1,2,4} would not be allowed since '3' is missing.
%o A252481 (PARI) is(n)={d=Set(digits(n));d[1]==1 || (#d>1&&d[2]==1) || return; d[#d]==#d-!d[1]}
%o A252481 (Python)
%o A252481 def ok(n):
%o A252481 s = set(str(n)); return '1' in s and len(s) == ord(max(s))-ord(min(s))+1
%o A252481 def aupto(nn): return [m for m in range(1, nn+1) if ok(m)]
%o A252481 print(aupto(1223)) # _Michael S. Branicky_, Jan 10 2021
%Y A252481 Cf. A032981, A050278, A033075, A010785, A108965, A134336, A252490.
%K A252481 nonn,base
%O A252481 1,2
%A A252481 _M. F. Hasler_, Dec 24 2014