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 A050257 #32 Feb 16 2025 08:32:40
%S A050257 0,0,0,299710
%N A050257 Number of distinct antimagic squares of order n (modulo rotations and reflections).
%C A050257 An Anti-Magic Square (AMS) is an arrangement of the numbers 1 to n*n in a square matrix such that the row, column and diagonal sums form a sequence of consecutive integers.
%C A050257 Cormie et al. estimated that the total number of 5 X 5 antimagic squares is on the order of 10^17. However, computational evidence suggests that the number of such squares is on the order of 10^15. Out of 19 billion randomly generated 5 X 5 matrices with distinct entries in {1, 2, ..., 25}, only 6 formed antimagic squares (see Examples below). - _John M. Campbell_, Nov 27 2022
%D A050257 J. Cormie, V. Linek, S. Jiang, and R.-C. Chen, Investigating the antimagic square, J. Combin. Math. Combin. Comput., 43 (2002), 175-197.
%H A050257 J. Cormie, <a href="http://www.uwinnipeg.ca/~vlinek/jcormie/index.html">The Anti-Magic Square Project</a>
%H A050257 J. Cormie, <a href="/A050257/a050257.gif">Example</a>: sorting the sums (numbers in black on the border) yields the sequence: 252, 253, 254, 255, 256, 257, 258, 259, 260, 261, 262, 263, 264, 265, 266, 267, 268, 269 (from web page above).
%H A050257 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/AntimagicSquare.html">Antimagic Square.</a>
%H A050257 <a href="/index/Mag#magic">Index entries for sequences related to magic squares</a>
%e A050257 The following are antimagic squares of order 5.
%e A050257 [22 7 20 1 18] [ 2 22 11 6 21]
%e A050257 [ 5 2 25 15 17] [ 3 24 15 8 20]
%e A050257 [13 19 6 24 3] [12 19 14 16 7]
%e A050257 [11 8 14 21 12] [18 1 9 23 13]
%e A050257 [16 23 4 9 10] [25 5 17 10 4]
%e A050257 .
%e A050257 [ 3 12 18 21 17] [13 12 19 4 18]
%e A050257 [23 5 9 4 25] [11 22 1 21 8]
%e A050257 [13 19 22 6 1] [ 6 20 3 25 16]
%e A050257 [16 14 8 24 2] [15 5 23 10 9]
%e A050257 [10 20 11 7 15] [24 2 14 7 17]
%e A050257 .
%e A050257 [ 3 24 4 20 18] [23 22 3 1 12]
%e A050257 [22 10 12 5 13] [21 9 17 13 7]
%e A050257 [17 1 21 25 6] [ 4 5 16 24 19]
%e A050257 [ 8 7 19 14 15] [ 2 10 25 11 18]
%e A050257 [ 9 23 11 2 16] [20 14 8 15 6]
%K A050257 nonn,bref,hard,nice
%O A050257 1,4
%A A050257 _Eric W. Weisstein_
%E A050257 a(n) not known for n >= 5.