Austrian economists are notorious for their rejection of mathematical models in economics. Considering this evidence that they can't count, we can guess what their REAL reason is.
Our monthly The Free Market examines the economic and political scene from a classical-liberal viewpoint. The Austrian Economics Newsletter links our academic network with in-depth interviews. The Mises Review surveys new books. The Quarterly Journal of Austrian Economics (the successor journal to the Review of Austrian Economics), is the premier setting for new research and ideas in economics. The Journal of Libertarian Studies is the scholarly venue for political theory and applications.
They say seven, but only list 5 (or 6 if you give them the benefit of the doubt.) Taken from About the Mises Institute.