The category of 3-computads is not cartesian closed

We show, using [A. Carboni, P.T. Johnstone, Connected limits, familial representability and Artin glueing, Math. Structures Comput. Sci. 5 (1995) 441–459] and Eckmann–Hilton argument, that the category of 3-computads is not cartesian closed. As a corollary we get that neither the category of all computads nor the category of n-computads, for n>2, do form locally cartesian closed categories, and hence elementary toposes.