Protein sequence space can be represented as a space with n dimensions, where n is the number of amino acids in the protein. Each axis has 20 positions representing the 20 amino acids. There are 400 possible 2 amino acid proteins (dipeptide) which can be arranged in a 2D grid. the 8000 tripeptides can be arranged in a 3D cube. There are an astronomical number of longer protein sequences which are arranged in large, multidimensional spaces.