 Since formula_65 has simple poles at the non-positive integers, it follows formula_59 has simple zeros at the nonpositive integers, and so the equation above becomes Weierstrass's formula with formula_67 in place of formula_68.The derivation of the constants formula_69 and formula_70 is somewhat technical, but can be accomplished by using some identities involving the Riemann zeta function (see this identity, for instance).See also the Weierstrass factorization theorem.