Prime number identification in idiots savants: can they calculate them?

Several idiots savants who were able to identify prime numbers have been reported. This ability requires complex calculations, because no simple algorithms are known for determining primes. Many savants, however, who demonstrate this ability, do not possess the arithmetical skills to perform such calculations. Explanations offered for the feats of idiots savants are reviewed in the light of their applicability to the cases of prime identification. Existing models cannot fully explain prime number identification for savants with weak arithmetical skills. The author shows that through the natural tendency of visual perception to be organized symmetrically, a distinction between prime and nonprime numbers can be made. This process could both explain the origin of the interest and the ability to identify prime numbers in mathematically weak savants.