EN
We use the Maurey-Rosenthal factorization theorem to obtain a new characterization of multiple 2-summing operators on a product of $l_{p}$ spaces. This characterization is used to show that multiple s-summing operators on a product of $l_{p}$ spaces with values in a Hilbert space are characterized by the boundedness of a natural multilinear functional (1 ≤ s ≤ 2). We use these results to show that there exist many natural multiple s-summing operators $T: l_{4/3} × l_{4/3} → l₂$ such that none of the associated linear operators is s-summing (1 ≤ s ≤ 2). Further we show that if n ≥ 2, there exist natural bounded multilinear operators $T: l_{2n/(n+1)} × ⋯ × l_{2n/(n+1)} → l₂$ for which none of the associated multilinear operators is multiple s-summing (1 ≤ s ≤ 2).