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 A116261 #13 Jul 18 2021 06:49:08 %S A116261 7,97,766,857,909,997,3284,6712,9997,45451,54545,99997,990099,999997, %T A116261 8181818,9999997,70588232,99999997,343130553,362637362,363636360, %U A116261 420053630,421052631,497975708,502024288,578947365,579946366 %N A116261 Numbers k such that k*(k+5) gives the concatenation of two numbers m and m-4. %Y A116261 Cf. A028557, A116130, A116255, A116260, A116262, A116268. %K A116261 nonn,base %O A116261 1,1 %A A116261 _Giovanni Resta_, Feb 06 2006