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 A045571 #9 Jan 11 2021 02:49:30 %S A045571 121,242,363,484,616,737,858,979,10901,11011,12221,13431,14641,15851, %T A045571 17171,18381,19591,20702,21912,22022,23232,24442,25652,26862,28182, %U A045571 29392,30503,31713,32923,33033,34243,35453,36663,37873,39193,40304 %N A045571 Numbers that are palindromic, divisible by 11 and have an odd number of digits. %C A045571 All the palindromic numbers with an even number of digits are divisible by 11. The number of palindromic numbers with 2*k+1 digits that are divisible by 11 is (10^(k+1) + (-1)^k)/11, and their asymptotic relative density within the set of all palindromic numbers with an odd number of digits (A056525) is 1/11 (Schmidt, 1988). - _Amiram Eldar_, Jan 11 2021 %H A045571 Amiram Eldar, <a href="/A045571/b045571.txt">Table of n, a(n) for n = 1..10000</a> %H A045571 Harvey Schmidt, Jr., <a href="https://www.jstor.org/stable/2689549">Palindromes: Density and Divisibility</a>, Mathematics Magazine, Vol. 61, No. 5 (1988), pp. 297-300. %t A045571 Select[11 * Range[4000], PalindromeQ[#] && OddQ[IntegerLength[#]] &] (* _Amiram Eldar_, Jan 11 2021 *) %Y A045571 Intersection of A056525 and A083852. %K A045571 base,nonn %O A045571 1,1 %A A045571 _Jeff Burch_