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 A321540 #18 Nov 12 2022 04:07:31
%S A321540 1,3,9,27,18,234,279,1278,1566,13689,4599,114777,113445,1233459,
%T A321540 2467899,1344789,1234467,11123469,23447889,1112246667,134446788,
%U A321540 12333456,113356899,11234477889,122234456889,23444678889,1222345568889,2445567778899
%N A321540 3^n with digits rearranged into nondecreasing order.
%F A321540 a(n) = A004185(A000244(n)). - _Michel Marcus_, Nov 10 2022
%t A321540 Table[FromDigits[Sort[IntegerDigits[3^n]]], {n, 0, 40}] (* _Vincenzo Librandi_, Jan 22 2020 *)
%o A321540 (Magma) [Seqint(Reverse(Sort(Intseq(3^n)))):n in [0..35]]; // _Vincenzo Librandi_, Jan 22 2020
%o A321540 (Python)
%o A321540 def A321540(n): return int(''.join(sorted(str(3**n)))) # _Chai Wah Wu_, Nov 10 2022
%Y A321540 The following are parallel families: A000079 (2^n), A004094 (2^n reversed), A028909 (2^n sorted up), A028910 (2^n sorted down), A036447 (double and reverse), A057615 (double and sort up), A263451 (double and sort down); A000244 (3^n), A004167 (3^n reversed), A321540 (3^n sorted up), A321539 (3^n sorted down), A163632 (triple and reverse), A321542 (triple and sort up), A321541 (triple and sort down).
%Y A321540 Cf. A004185.
%K A321540 nonn,base
%O A321540 0,2
%A A321540 _N. J. A. Sloane_, Nov 19 2018