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 A049475 #37 Feb 16 2025 08:32:40
%S A049475 1,4,39,2260,1338614,8522456190
%N A049475 Number of 2n X 2n matrices whose entries are {0,-1,+1} and whose row sums and column sums are all distinct.
%C A049475 Matrices differing by taking transpose, multiplying by -1 and permuting rows and columns are regarded as equivalent.
%D A049475 It is known (see references) that a (2n+1) X (2n+1) matrix of this form cannot exist.
%D A049475 Rainer Bodendiek, Gustav Burosch; Streifzüge durch die Kombinatorik, Aufgaben und Lösungen aus dem Schatz der Mathematik-Olympiaden, (Excursions into Combinatorics) Spektrum Akademischer Verlag, Heidelberg, 1995, ISBN 3-86025-393-X Kapitel: Aufgaben zu Invarianten, Aufgabe 5.30, pp. 250-253.
%D A049475 Fred Galvin, posting to sci.math, Date: 1999-09-25 - Solution to the antimagic 0,1,-1 matrix problem.
%H A049475 Denis Cazor, <a href="/A049475/a049475_4.pdf">Notes for a talk</a>
%H A049475 Denis Cazor, <a href="/A049475/a049475_5.pdf">Programme Pascal</a>
%H A049475 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/IntegerMatrix.html">Integer Matrix</a>
%e A049475 A 2 X 2 example: [ 1 1; 0 -1 ].
%Y A049475 Cf. A049526, A049527.
%K A049475 nonn,nice,hard
%O A049475 1,2
%A A049475 _Michael Kleber_
%E A049475 Bodendiek-Burosch reference from torsten.sillke(AT)lhsystems.com
%E A049475 a(6) from _Denis Cazor_, Dec 06 2017