  The congruent number elliptic curves are defined by $E_d: y^2=x^3-d^2x$,
where $d\in \mathbb{N}.$ We give a simple proof of a formula for
$L(\mathrm{Sym}^2(E_d),3)$ in terms of the determinant of the elliptic
trilogarithm evaluated at some degree zero divisors supported on the torsion
points on $E_d(\overline{\mathbb{Q}})$.
