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 A110201 #6 Aug 22 2021 19:29:44
%S A110201 1,9,70,535,3906,29274,215900,1628175,12197570,92830430,704127060,
%T A110201 5400199350,41331491124,318871044756,2456608834680,19039140186495,
%U A110201 147401590706370,1146463189301430,8909683732878500,69495629981713650
%N A110201 a(n) = sum of squares of numbers < 2^n having exactly [n/2]+1 ones in their binary expansion.
%C A110201 a(n) equals the largest term in row n of triangle A110200.
%F A110201 a(n) = (4^n-1)/3*C(n-2, n\2) + (2^n-1)^2*C(n-2, n\2-1).
%t A110201 Join[{1},Table[Total[Select[Range[2^n],DigitCount[#,2,1]==Floor[ n/2]+ 1&]^2],{n,2,20}]] (* _Harvey P. Dale_, Aug 22 2021 *)
%o A110201 (PARI) a(n)=(4^n-1)/3*binomial(n-2,n\2)+(2^n-1)^2*binomial(n-2,n\2-1)
%Y A110201 Cf. A110200 (triangle), A002450 (column 1), A110202 (column 2), A110203 (column 3), A110204 (column 4).
%K A110201 nonn
%O A110201 1,2
%A A110201 _Paul D. Hanna_, Jul 16 2005