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 A381917 #23 Mar 18 2025 15:16:12 %S A381917 55,99,5050,7272,7777,9999,500500,648648,851851,999999,13641364, %T A381917 24752475,25252525,36363636,50005000,61116111,88888888,99999999, %U A381917 1111111111,3888938889,4132841328,5000050000,5243952439,9756097560,9999999999,159341159341,175676175676,233415233415 %N A381917 Kaprekar numbers that are the concatenation of two equal numbers. %C A381917 All repdigit numbers of even length which are Kaprekar numbers are terms. Since 99, 9999, 999999, ... and 5050, 500500, 50005000, ... are Kaprekar numbers, there are infinitely many terms. %H A381917 Shyam Sunder Gupta, <a href="/A381917/b381917.txt">Table of n, a(n) for n = 1..2163</a> %H A381917 Shyam Sunder Gupta, <a href="https://doi.org/10.1007/978-981-97-2465-9_9">On Some Marvellous Numbers of Kaprekar</a>, Exploring the Beauty of Fascinating Numbers, Springer (2025) Ch. 9, 275-315. %e A381917 648648 is a Kaprekar number which is the concatenation of 648 and 648. %Y A381917 Intersection of A006886 and A020338. %Y A381917 Cf. A092118. %K A381917 base,nonn %O A381917 1,1 %A A381917 _Shyam Sunder Gupta_, Mar 10 2025