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 A054215 #17 Oct 17 2019 20:01:50 %S A054215 8281,82428241,98029801,538277538276,998002998001,7783702677837025, %T A054215 9998000299980001,79225472657922547264,86432513458643251344, %U A054215 92237976109223797609,99998000029999800001,106710893290106710893289 %N A054215 Squares that are concatenations of two consecutive decreasing numbers. %C A054215 Infinitely many terms of this sequence are provided by A168624(k)^2 for k>0. - _Bruno Berselli_, Mar 13 2018 %D A054215 Luca, Florian, and Pantelimon Stănică. "Perfect Squares as Concatenation of Consecutive Integers." The American Mathematical Monthly 126.8 (2019): 728-734. %F A054215 a(n) = concatenation of A054214(n) and A054214(n)-1. - _Max Alekseyev_, May 14 2007 %e A054215 E.g. '8242' + '8242-1' gives 82428241 which is 9079^2. %Y A054215 Cf. A054214, A054216, A030465, A030466, A030467, A020339, A020340. %K A054215 nonn,base %O A054215 1,1 %A A054215 _Patrick De Geest_, Feb 15 2000 %E A054215 More terms from _Max Alekseyev_, May 14 2007 %E A054215 82848241 corrected to 82428241 by _Dominick Cancilla_, Jul 21 2010