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 A247264 #9 Sep 14 2014 00:22:34 %S A247264 15,75,11252109375,375, %T A247264 9694963627295445503856592180983186990852118469774723052978515625, %U A247264 6841439843263141047421876154427540653587129781953990459442138671875 %N A247264 Smallest positive number not divisible by 10 whose square remains a square when prefixed with 10^n. %e A247264 a(0) = 15 since 15^2 = 225 and 1225 is square and 15 is the smallest number not ending in 0 with this property. a(3) = 375 since 375^2 = 140625 and 1000140625 is square and 375 is the smallest number not ending in 0 with this property. %o A247264 (PARI) %o A247264 a(n)=k=1;while(k^2%100==0||!issquare(10^(#Str(k^2)+n)+k^2),k++);k^2 %o A247264 n=0;while(n<10,print1(a(n),", ");n++) \\ _Derek Orr_, Sep 13 2014 %Y A247264 Cf. A242268, A247261, A247262, A247263, A247312. %K A247264 nonn,base %O A247264 0,1 %A A247264 _Chai Wah Wu_, Sep 11 2014