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.
a(2) = -4: 1, 2; 2, 0. a(3) = -74: 1, 3, 4; 3, 4, 0; 4, 0, 2. a(4) = -1297: 3, 2, 6, 0; 2, 6, 0, 1; 6, 0, 1, 4; 0, 1, 4, 5.
a(2) = 2: 2, 0; 0, 1. a(3) = 31: 1, 4, 2; 4, 2, 3; 2, 3, 0. a(4) = 1781: 1, 2, 5, 6; 2, 5, 6, 0; 5, 6, 0, 4; 6, 0, 4, 3.
a[n_] := CountDistinct[Table[Det[HankelMatrix[Join[Drop[per = Part[Permutations[Range[0, 2 n - 2]], i], n],{Part[per, n]}], Join[{Part[per, n]}, Drop[per, - n]]]], {i, (2 n - 1) !}]]; Join[{1},Array[a, 5]]
a(n) = my(v=[0..2*n-2], list=List()); forperm(v, p, listput(list, matdet(matrix(n, n, i, j, p[i+j-1])));); #Set(list); \\ Michel Marcus, Feb 08 2024
from itertools import permutations from sympy import Matrix def A369944(n): return len({Matrix([p[i:i+n] for i in range(n)]).det() for p in permutations(range((n<<1)-1))}) # Chai Wah Wu, Feb 12 2024
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