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 A261177 #14 Nov 26 2015 08:40:53
%S A261177 0,10,180,1392,6149,21350,57192,137617,298864,593378,1101739,1936342,
%T A261177 3216080
%N A261177 Maximum value of (1/2)*Sum_{i=1..n} Sum_{j=1..n} Sum_{k=1..n} Sum_{l=1..n} gcd(b(i,j),b(k,l)) * ((i-k)^2+(j-l)^2) for an n X n matrix b filled with the integers 1 to n^2.
%C A261177 Best results found in Al Zimmermann's Programming Contest "Delacorte Numbers". For more information see A261176. All terms beyond a(5) are conjectured based on numerical results. Terms up to a(11) have at least 5 independent verifications. Lower bounds for the next terms are a(14)>=5189492, a(15)>=8110781, a(16)>=12239616, a(17)>=18073562, a(18)>=26055061, a(19)>=36769303, a(20)>=51095165.
%H A261177 Al Zimmermann's Programming Contests, <a href="http://azspcs.com/Contest/DelacorteNumbers">Delacorte Numbers</a>, Description, October 2014.
%H A261177 Al Zimmermann's Programming Contests, <a href="http://azspcs.com/Contest/DelacorteNumbers/FinalReport">Delacorte Numbers</a>, Final Report, January 2015.
%e A261177 a(3)=180, because no arrangement of the matrix elements exists that produces a larger Delacorte Number than e.g. ((2 3 4)(9 1 5)(8 7 6)).
%Y A261177 Cf. A261176, A003989, A018782.
%K A261177 nonn,hard
%O A261177 1,2
%A A261177 _Hugo Pfoertner_, Aug 15 2015
%E A261177 Lower bounds for a(18) and a(20) improved by _Hugo Pfoertner_, Nov 22 2015