OFFSET
1,2
FORMULA
From Vaclav Kotesovec, Apr 16 2018: (Start)
a(n) = 5^(n + 1) * Gamma(n) * Gamma(n + 7/5) / (7 * Gamma(2/5) * 2^n).
a(n) ~ Pi * 5^(n+1) * n^(2*n + 2/5) / (7 * Gamma(2/5) * 2^(n-1) * exp(2*n)).
a(n+1) = a(n) * n*(5*n + 7)/2.
(End)
EXAMPLE
The matrix begins:
1 1 1 1 1 1 1 ...
1 7 1 1 1 1 1 ...
1 1 18 1 1 1 1 ...
1 1 1 34 1 1 1 ...
1 1 1 1 55 1 1 ...
1 1 1 1 1 81 1 ...
1 1 1 1 1 1 112 ...
MAPLE
d:=(i, j)->`if`(i<>j, 1, i*(5*i-3)/2):
seq(LinearAlgebra[Determinant](Matrix(n, d)), n=1..20);
MATHEMATICA
nmax = 20; Table[Det[Table[If[i == j, i*(5*i - 3)/2, 1], {i, 1, k}, {j, 1, k}]], {k, 1, nmax}] (* Vaclav Kotesovec, Apr 16 2018 *)
Table[FullSimplify[5^(n + 1) * Gamma[n] * Gamma[n + 7/5] / (7 * Gamma[2/5] * 2^n)], {n, 1, 15}] (* Vaclav Kotesovec, Apr 16 2018 *)
PROG
(PARI) a(n) = matdet(matrix(n, n, i, j, if (i!=j, 1, i*(5*i-3)/2))); \\ Michel Marcus, Apr 16 2018
CROSSREFS
Cf. A000566 (heptagonal numbers).
KEYWORD
nonn
AUTHOR
Muniru A Asiru, Apr 15 2018
STATUS
approved