A362073 a(n) is the permanent of the n X n symmetric matrix M(n) whose generic element M[i,j] = digsum(i*j).
1, 1, 8, 216, 7344, 168183, 7226091, 506792295, 43261224876, 5520748306176, 170835815638728, 19632554202684096, 2228687316428293152, 347514692118635694888, 62201193604462666921968, 8113764691750577654439864, 1557556394182730485102253088, 348394812690307787609428395792
Offset: 0
Examples
a(6) = 7226091:
[1, 2, 3, 4, 5, 6]
[2, 4, 6, 8, 1, 3]
[3, 6, 9, 3, 6, 9]
[4, 8, 3, 7, 2, 6]
[5, 1, 6, 2, 7, 3]
[6, 3, 9, 6, 3, 9]
Programs
-
Mathematica
M[i_, j_]:=Total[IntegerDigits[i*j]]; Join[{1}, Table[Permanent[Table[M[i, j], {i, n}, {j, n}]], {n, 18}]] -
PARI
a(n) = matpermanent(matrix(n, n, i, j, sumdigits(i*j))); \\ Michel Marcus, Apr 08 2023
Formula
Sum_{i=1..n} M[n-i+1,i] = A362072(n).
Comments