Full Idea
Brouwer made the rather extraordinary claim that mathematics is a mental activity which uses no language.
Gist of Idea
Mathematics is a mental activity which does not use language
Source
report of Luitzen E.J. Brouwer (Mathematics, Science and Language [1928]) by David Bostock - Philosophy of Mathematics 7.1
Book Reference
Bostock,David: 'Philosophy of Mathematics: An Introduction' [Wiley-Blackwell 2009], p.200
A Reaction
Since I take language to have far less of a role in thought than is commonly believed, I don't think this idea is absurd. I would say that we don't use language much when we are talking!