Mathematical Diversions

A collection of mathematical miscellany that diverts me from my main research interests. Some of the posts are interesting (to me) mathematical problems with their solutions. Others are mostly recreational things that distracted me at one time or another. The intended audience for posts in this category are my sole self, and so I make no great effort to polish the writing. Do send me an email with questions if you find anything here interesting or confusing.

Can initial data for Einstein's equation be specified in such a way that all the 'energy' are kinetic and not potential?

When does the decimal expansion of a number end with one digit repeated?

It is fairly well known that experts in partial differential equations and experts in harmonic analysis prefer to define the Fourier …

A bit of trivia (can't think of any use of it now) Theorem   Let $(M,g)$ be a two-dimensional compact Riemannian manifold with …

First let us consider the following question on a finite dimensional vector space. Let $(V, \langle\cdot\rangle)$ be a $k$-dimensional …