The 2-summing norm of computed with n vectors

The 2-summing norm of an n-dimensional Banach space computed with n vectors is known to belong between and . It is shown that the 2-summing norm of real computed with three vectors is 5/3. Some lower estimates for 2-summing norms of computed with n vectors are stated, which are considerably better than universal ones and are based on the existence of certain block designs or Hadamard matrices