Miller Lab Alumnus Andreas Nieder tells you everything you need to know about the brain substrates of the sense of number:

Nieder, Andreas. “The neuronal code for number.” Nature Reviews Neuroscience (2016).

 

 

Eiselt and Nieder show that coding of numerical magnitudes is the prefrontal cortex but not the premotor or cingulate cortex.

Eiselt, Anne-Kathrin, and Andreas Nieder. “Single-cell coding of sensory, spatial and numerical magnitudes in primate prefrontal, premotor and cingulate motor cortices.” Experimental brain research (2015): 1-14.

Miller Lab alumnus, Andreas Nieder, shows number tuned neurons in pefrontal and parietal cortices of naive (untrained) subjects.
Viswanathan and Nieder 2013 

Andreas Nieder’s Miller Lab work on the neural substrates for numerosity:

Nieder, A., Freedman, D.J., and Miller, E.K. (2002) Representation of the quantity of visual items in the primate prefrontal cortex.  Science. 297:1708-1711. View PDF »

Nieder, A. and Miller, E.K. (2003) Coding of cognitive magnitude: Compressed scaling of numerical information in the primate prefrontal cortex. Neuron. 37:149-157. View PDF »

Nieder, A. and Miller, E.K. (2004) A parieto-frontal network for visual numerical information in the monkey. Proceedings of the National Academy of Sciences, 101:7457-7462. View PDF »

Nieder, A. and Miller, E.K. (2004) Analog numerical representations in rhesus monkeys: Evidence for parallel processing. Journal of Cognitive Neuroscience. 16:889-901. View PDF »