OFFSET
1,2
FORMULA
a(n) = (n + 1/2) * (2*n-1)! / (3 * 2^(n-2)). - Vaclav Kotesovec, Apr 16 2018
EXAMPLE
The matrix begins:
1 1 1 1 1 1 1 ...
1 6 1 1 1 1 1 ...
1 1 15 1 1 1 1 ...
1 1 1 28 1 1 1 ...
1 1 1 1 45 1 1 ...
1 1 1 1 1 66 1 ...
1 1 1 1 1 1 91 ...
MAPLE
d:=(i, j)->`if`(i<>j, 1, i*(2*i-1)):
seq(LinearAlgebra[Determinant](Matrix(n, d)), n=1..20);
MATHEMATICA
nmax = 20; Table[Det[Table[If[i == j, i*(2*i - 1), 1], {i, 1, k}, {j, 1, k}]], {k, 1, nmax}] (* Vaclav Kotesovec, Apr 16 2018 *)
Table[(n + 1/2) * (2*n - 1)! / (3 * 2^(n - 2)), {n, 1, 20}] (* Vaclav Kotesovec, Apr 16 2018 *)
Table[Det[DiagonalMatrix[PolygonalNumber[6, Range[n]]]/.(0->1)], {n, 20}] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Mar 23 2020 *)
PROG
(PARI) a(n) = matdet(matrix(n, n, i, j, if (i!=j, 1, i*(2*i-1)))); \\ Michel Marcus, Apr 16 2018
CROSSREFS
Cf. A000384 (hexagonal numbers).
Cf. Determinant of n X n matrix whose main diagonal consists of the first n k-gonal numbers and all other elements are 1's: A000142 (k=2), A067550 (k=3), A010791 (k=4, with offset 1), A302909 (k=5), this sequence (k=6), A302911 (k=7), A302912 (k=8), A302913 (k=9), A302914 (k=10).
Odd bisection of column k=1 of A097591.
KEYWORD
nonn
AUTHOR
Muniru A Asiru, Apr 15 2018
STATUS
approved