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 A043074 #7 May 19 2023 13:42:04
%S A043074 1,4,28,29,30,31,32,33,34,35,36,244,254,264,274,284,294,304,314,324,
%T A043074 2188,2197,2206,2215,2224,2233,2242,2251,2260,2270,2279,2288,2297,
%U A043074 2306,2315,2324,2333,2342,2352,2361,2370,2379,2388,2397
%N A043074 a(n)=(s(n)+6)/9, where s(n)=n-th base 9 palindrome that starts with 3.
%t A043074 b9pQ[n_]:=Module[{idn9=IntegerDigits[9n-6,9]},idn9==Reverse[idn9]&&idn9[[1]]==3]; Select[ Range[2500],b9pQ] (* _Harvey P. Dale_, May 19 2023 *)
%K A043074 nonn,base
%O A043074 1,2
%A A043074 _Clark Kimberling_