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 A386974 #7 Aug 15 2025 18:18:38
%S A386974 1,1,5,42,480,6875,117936,2352980,53477376,1363146165,38500000000,
%T A386974 1193121531646,40246286745600,1467779362716303,57544321060925440,
%U A386974 2413281884765625000,107798160680740192256,5109425146945021190505,256115971082717276995584,13536555538728461399269330
%N A386974 a(n) is the permanent of the symmetric n X n matrix M_n where M_n(j,k) = n for j = k, M_n(j,n) = n-j, M_n(n,k) = n-k, M_n(j,k) = 0 otherwise.
%e A386974 a(5) = permanent(M_5) = 6875 where M_5 is the matrix
%e A386974 [5 0 0 0 4]
%e A386974 [0 5 0 0 3]
%e A386974 [0 0 5 0 2]
%e A386974 [0 0 0 5 1]
%e A386974 [4 3 2 1 5]
%t A386974 M[j_, k_, n_]:=If[j==k, n, If[k==n, n-j, If[j==n, n-k, 0]]]; a[n_]:=Permanent[Table[M[i, j, n], {i, n}, {j, n}]];Join[{1}, Array[a, 18]]
%o A386974 (PARI) a(n) = matpermanent(matrix(n, n, j, k, if (j==k, n, if (k==n, n-j, if (j==n, n-k, 0))))); \\ _Michel Marcus_, Aug 12 2025
%Y A386974 Cf. A174963 (determinants), A386975.
%K A386974 nonn
%O A386974 0,3
%A A386974 _Stefano Spezia_, Aug 11 2025