[HPsquared]

I'd never thought about it in this way before but the idea of writing a number as a decimal (or other) string of numerals, bears some resemblance to a Fourier transform.

Think of the components of a written number: ones, tens, hundreds etc which have a repeating pattern. Digits are inherently periodic. Not too far from periodic basis functions.

Both involve breaking something down into periodic components, and reversing the process by adding up the components.

[IAmBroom]

Clever, but only really appropriate for the most significant digit.

The one's digit gives info about parity (odd/even), but nothing else.