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 A023797 #20 Feb 16 2025 08:32:34
%S A023797 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,32,33,48,49,50,64,65,66,67,
%T A023797 80,81,82,83,84,96,97,98,99,100,101,112,113,114,115,116,117,118,128,
%U A023797 129,130,131,132,133,134,135,144,145,146,147,148,149,150,151,152
%N A023797 Katadromes: digits in base 16 are in strict descending order.
%C A023797 There are 65535 terms, with a(65535) = 18364758544493064720 = FEDCBA9876543210_16. - _Michael S. Branicky_, Feb 05 2024
%H A023797 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Digit.html">Digit</a>.
%H A023797 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Katadrome.html">Katadrome</a>.
%t A023797 Select[Range[0,200],Max[Differences[IntegerDigits[#,16]]]<0&] (* _Harvey P. Dale_, Oct 23 2022 *)
%o A023797 (Python)
%o A023797 from itertools import combinations, islice
%o A023797 def agen(): # generator of terms
%o A023797 yield 0
%o A023797 for d in range(1, 17):
%o A023797 yield from sorted(int("".join(c), 16) for c in combinations("FEDCBA9876543210", d) if c[0] != '0')
%o A023797 print(list(islice(agen(), 50))) # _Michael S. Branicky_, Feb 05 2024
%K A023797 nonn,base,fini,easy
%O A023797 1,3
%A A023797 _Olivier Gérard_