We consider positive solutions u of the semilinear biharmonic equation
Δ2u=∣x∣−2n+4g(∣x∣2n−4u) in Rn∖{0} with non-removable singularities at the origin. Under natural
assumptions on the nonlinearity g, we show that ∣x∣2n−4u is a
periodic function of ln∣x∣ and we classify all such solutions.Comment: To V. Maz'ya on the occasion of his 80th birthday; references adde