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 A381918 #20 Mar 18 2025 15:25:48 %S A381918 45,2223,2728,4950,148149,351352,499500,11111112,38883889,49995000, %T A381918 63636364,74747475,75247525,86358636,4756047561,4999950000,5867158672, %U A381918 6111061111,8888888889,9132791328,104247104248,164983164984,178321178322,195156195157,230769230770,269230269231 %N A381918 Kaprekar numbers that are the concatenation of two consecutive numbers. %C A381918 Since all numbers 4950, 449500, 49995000, ... are Kaprekar numbers, there are infinitely many terms. %H A381918 Shyam Sunder Gupta, <a href="/A381918/b381918.txt">Table of n, a(n) for n = 1..2143</a> %H A381918 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 A381918 If the number 351 is concatenated with the next number, 352, we get a Kaprekar number, 351352. It can be verified that 351352^2 = 123448227904, and 123448 + 227904 = 351352. %Y A381918 Intersection of A006886 and A001704. %Y A381918 Cf. A030466. %K A381918 base,nonn %O A381918 1,1 %A A381918 _Shyam Sunder Gupta_, Mar 10 2025