We consider the Volterra integral operator T:L-P(R+)-->L-P(R+) defined
(Tf)(x)=v(x)integral(0)(x) u(t)f(t) dt. Under suitable conditions on
u. and v, upper and lower estimates for the approximation numbers a(n)
(T) of T are established when 1<p<infinity. When p=2, these yield limn
-->infinity na(n)(T)=pi(-1)integral(0)(infinity) \u(t)v(t)\dt. We also
provide upper and lower estimates for the l(alpha) and weak l(alpha)
norms of (a(n)(T)) when 1<alpha<infinity.