A369945 - OEIS

%I #18 Feb 12 2024 13:42:19

%S 1,1,3,39,1710,128502,13644965

%N a(n) is the number of distinct values of the permanent of an n X n Hankel matrix using the integers 0 to 2*(n - 1).

%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Hankel_matrix">Hankel matrix</a>.

%t a[n_] := CountDistinct[Table[Permanent[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]]

%o (PARI) a(n) = my(v=[0..2*n-2], list=List()); forperm(v, p, listput(list, matpermanent(matrix(n, n, i, j, p[i+j-1])));); #Set(list); \\ _Michel Marcus_, Feb 08 2024

%o (Python)

%o from itertools import permutations

%o from sympy import Matrix

%o def A369945(n): return len({Matrix([p[i:i+n] for i in range(n)]).per() for p in permutations(range((n<<1)-1))}) # _Chai Wah Wu_, Feb 12 2024

%Y Cf. A358569, A358570.

%K nonn,hard,more

%O 0,3

%A _Stefano Spezia_, Feb 06 2024

%E a(6) from _Michel Marcus_, Feb 08 2024