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 A369942 #17 Feb 12 2024 13:44:22
%S A369942 1,1,3,49,1480,50522,2517213
%N A369942 a(n) is the number of distinct values of the determinant of an n X n Hankel matrix using the integers 1 to 2*n - 1.
%H A369942 Wikipedia, <a href="https://en.wikipedia.org/wiki/Hankel_matrix">Hankel matrix</a>.
%t A369942 a[n_] := CountDistinct[Table[Det[HankelMatrix[Join[Drop[per = Part[Permutations[Range[2 n - 1]], i], n],{Part[per, n]}], Join[{Part[per, n]}, Drop[per, - n]]]], {i, (2 n - 1) !}]]; Join[{1}, Array[a, 5]]
%o A369942 (PARI) a(n) = my(v=[1..2*n-1], list=List()); forperm(v, p, listput(list, matdet(matrix(n, n, i, j, p[i+j-1])));); #Set(list); \\ _Michel Marcus_, Feb 08 2024
%o A369942 (Python)
%o A369942 from itertools import permutations
%o A369942 from sympy import Matrix
%o A369942 def A369942(n): return len({Matrix([p[i:i+n] for i in range(n)]).det() for p in permutations(range(1,n<<1))}) # _Chai Wah Wu_, Feb 12 2024
%Y A369942 Cf. A350931, A368351, A368352.
%K A369942 nonn,hard,more
%O A369942 0,3
%A A369942 _Stefano Spezia_, Feb 06 2024
%E A369942 a(6) from _Michel Marcus_, Feb 08 2024