Lewis Carroll's formula for calendar calculating.

One of the extraordinary skills occasionally displayed by individuals of low intelligence (so-called idiots savants) is the ability to name, within seconds, the day of the week for any given date, sometimes over a range of centuries. A number of scholarly papers contain references to formulas that can be used in making this calculation, but none cites one of the earliest published methods, that of Lewis Carroll. However, formulas such as Carroll's are too complex to be self-taught by idiots savants and, consequently, cannot account for their remarkable performance. Alternative explanatory hypotheses were briefly discussed.