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 A009993 #42 Feb 16 2025 08:32:32
%S A009993 0,1,2,3,4,5,6,7,8,9,12,13,14,15,16,17,18,19,23,24,25,26,27,28,29,34,
%T A009993 35,36,37,38,39,45,46,47,48,49,56,57,58,59,67,68,69,78,79,89,123,124,
%U A009993 125,126,127,128,129,134,135,136,137,138,139,145,146,147,148,149,156,157
%N A009993 Numbers whose decimal digits are in strictly increasing order.
%C A009993 Sequence has 512 terms, since every term except 0 corresponds to a nonempty subset of {1,2,3,4,5,6,7,8,9}.
%C A009993 A178788(a(n)) = 1. - _Reinhard Zumkeller_, Jun 30 2010
%C A009993 Number of terms in [10^(n-1), 10^n): 0, 9, 36, 84, 126, 126, 84, 36, 9, 1. - _Robert G. Wilson v_, Jul 20 2014
%H A009993 Zak Seidov, <a href="/A009993/b009993.txt">Table of n, a(n) for n = 1..512</a> (full sequence)
%H A009993 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Digit.html">Digit</a>
%t A009993 Flatten@Table[FromDigits/@Subsets[Range[1, 9], {n}], {n, 0, 9}] (* _Zak Seidov_, May 19 2006 *)
%o A009993 (PARI) is_A009993(n)=Set(n=digits(n))==n \\ _M. F. Hasler_, Dec 11 2019
%o A009993 (PARI) forsubset(9,s,print1(fromdigits(Vec(s))",")) \\ _M. F. Hasler_, Dec 11 2019
%o A009993 (Python)
%o A009993 from itertools import combinations
%o A009993 def afull(): return [0] + sorted(int("".join(c)) for d in range(1, 10) for c in combinations("123456789", d))
%o A009993 print(afull()) # _Michael S. Branicky_, Sep 16 2022
%Y A009993 Cf. A009995.
%K A009993 nonn,fini,full,base
%O A009993 1,3
%A A009993 _N. J. A. Sloane_