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 A118872 #23 Nov 25 2022 07:21:37
%S A118872 0,1,2,3,4,5,9,10,11,13,16,17,21,27,31,35,36,39,114,119,973,1005,1010,
%T A118872 1025,3006,3029,3040,9128,9215,9227,9316,27431,27442,27515,27519,
%U A118872 27554,82632,82746,82763,82784,83111,246838,247206,247388,247406,247447,741310,742154
%N A118872 Numbers k such that digit sum of 3^k is a power of 3.
%C A118872 a(47) > 677750. - _Ray Chandler_, Jun 16 2006
%C A118872 a(47) <= 741310. If a(47) < 741310 then a(47) < 720000. a(48) <= 742154. If a(48) < 741310 then a(48) < 720000. - _David A. Corneth_, Nov 23 2022
%F A118872 A067500(n) = 3^a(n).
%e A118872 3^39 = 4052555153018976267 with digit sum 81 = 3^4, so 39 is a term.
%t A118872 Do[If[IntegerQ[Log[3, Plus @@ IntegerDigits[3^n]]], Print[n]], {n, 0, 677750}];
%o A118872 (PARI) is(n) = my(s = sumdigits(3^n)); s == 3^logint(s, 3) \\ _David A. Corneth_, Nov 23 2022
%Y A118872 Cf. A004166 (sum of digits of 3^n).
%K A118872 base,nonn
%O A118872 1,3
%A A118872 _Zak Seidov_, May 24 2006
%E A118872 Extended by _Ray Chandler_, Jun 16 2006
%E A118872 a(47) and a(48) from _Jon E. Schoenfield_, Nov 25 2022