login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Base-10 palindromes that start with 7.
4

%I #16 Aug 22 2021 14:55:56

%S 7,77,707,717,727,737,747,757,767,777,787,797,7007,7117,7227,7337,

%T 7447,7557,7667,7777,7887,7997,70007,70107,70207,70307,70407,70507,

%U 70607,70707,70807,70907,71017,71117,71217,71317,71417,71517,71617,71717,71817,71917

%N Base-10 palindromes that start with 7.

%C 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 Jaroslav Krizek, <a href="/A043042/b043042.txt">Table of n, a(n) for n = 1..2222</a>

%t 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 Select[Range[72000],First[IntegerDigits[#]]==7&&PalindromeQ[#]&] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Mar 02 2018 *)

%Y Cf. A002113.

%K nonn,base

%O 1,1

%A _Clark Kimberling_