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 A116121 #12 Sep 14 2023 00:46:46 %S A116121 65,6653,9605,218413,283720,996005,58446925,99960005,6086712229, %T A116121 7385370133,8478948853,9999600005,120178240093,161171620229, %U A116121 358247912200,426843573160,893417179213,999996000005,23376713203604 %N A116121 Numbers k such that k concatenated with k-5 gives the product of two numbers which differ by 2. %C A116121 Duplicate of A115432. See proof at A115432. - _Robert Israel_, Sep 13 2023 %e A116121 9999600005//9999600000 = 9999800000 * 9999800002, where // denotes concatenation. %Y A116121 Cf. A116116, A116120, A116122, A115431, A116252. %K A116121 nonn,base %O A116121 1,1 %A A116121 _Giovanni Resta_, Feb 06 2006