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 A128826 #16 Mar 31 2012 14:40:14
%S A128826 1,39,144,1756,49116,484471,4175271,38053824,10649244,1064924400,
%T A128826 43246886799,529955487744,2399106211776,50173961567511,
%U A128826 590207432515431,2099745368512359,20237877241133151,126421128012287511
%N A128826 a(n) = 10^(2n-1) minus largest square less than 10^(2n-1).
%C A128826 For even indices a(2k) = 2*10^k-1, hence only odd powers of 10 are considered in this sequence.
%H A128826 Hugo Pfoertner, <a href="/A128826/b128826.txt">Table of n, a(n) for n = 1..500</a>
%F A128826 a(n)=10^(2n-1)-A061433(2n-1).
%F A128826 a(n) = 10^(2*n-1) - floor(sqrt(10^(2*n-1)))^2.
%e A128826 a(1) = 1 because 10 - 3^2 = 1.
%e A128826 a(2) = 39 because 1000 - 31^2 = 39.
%e A128826 a(3) = 144 because 100000 - 316^2 = 144.
%t A128826 Table[10^n-Floor[(10^n-1)^(1/2)]^2,{n,1,40,2}]
%Y A128826 Cf. A061433, A051221.
%K A128826 nonn
%O A128826 1,2
%A A128826 _Zak Seidov_, Apr 12 2007