I was browsing wikipedia where I came across self-enumerating pangrams which are sentences that describe exactly the number of letters in itself. As per the wikipedia page on pangrams, Lee Sallows came up with one of the first self-enumerating pangrams, in 1984. In fact, he constructed a machine for this task when solving the problem through software alone failed.
As for pangrams, they are sentences using every letter of the alphabet atleast once, with perfect pangrams being sentences in which each alphabet appears exactly once. A well known English pangram is The quick brown fox jumps over the lazy dog.
I also found some information on another interesting piece – golygons – when I was looking for more information on Lee Sallows, who invented them. Golygons are polygons with side lengths as consecutive integers and all right angles.