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 A043042 #20 Sep 01 2025 23:44:08
%S A043042 7,77,707,717,727,737,747,757,767,777,787,797,7007,7117,7227,7337,
%T A043042 7447,7557,7667,7777,7887,7997,70007,70107,70207,70307,70407,70507,
%U A043042 70607,70707,70807,70907,71017,71117,71217,71317,71417,71517,71617,71717,71817,71917
%N A043042 Base-10 palindromes that start with 7.
%C A043042 Subsequence of A002113 (palindromic numbers). Union of A222727 (palindromic primes starting with a digit 7) and A222728 (palindromic composite numbers starting with a digit 7). - _Jaroslav Krizek_, Mar 12 2013
%H A043042 Jaroslav Krizek, <a href="/A043042/b043042.txt">Table of n, a(n) for n = 1..2222</a>
%t A043042 palQ[n_Integer, base_Integer] := Module[{idn = IntegerDigits[n, base]}, idn == Reverse[idn]]; Select[Range[0, 100000], IntegerDigits[#][[1]] == 7 && palQ[#, 10] &] (* _T. D. Noe_, Mar 12 2013 *)
%t A043042 Select[Range[72000],First[IntegerDigits[#]]==7&&PalindromeQ[#]&] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Mar 02 2018 *)
%Y A043042 Cf. A002113.
%K A043042 nonn,base,changed
%O A043042 1,1
%A A043042 _Clark Kimberling_