I remember a story whose title escapes me (I think by Isaac Asimov) where in the far future all math is done on calculators, and the ability to do "paper and pencil" math is considered a military secret.

Who knows how useful mental math will be when we can whistle up answers from brain implants someday? Before man discovered the written word, our ancestors were capable of immense feats of memory, like the "griot" from "Roots" or the ancient bards, who committed many thousands of lines of detailed information to memory. This talent seems largely lost in civilized nations, but we do without it.

For the record, I'm forcing my kids to learn "mental math." So I'm old-fashioned.