a(n) = (-1)^n*permanent[tan(Pi*(j+k)/(2n+1))]_{1<=j,k<=2n}.

A346162

a(n) = (-1)^n*permanent[tan(Pi*(j+k)/(2n+1))]_{1<=j,k<=2n}.

Terms

    a(0) =3a(1) =65a(2) =1995a(3) =149121a(4) =13399155a(5) =2141638785a(6) =387394882875

External references