Poetry, in other words, is mathematics. It is close to a particular branch of the subject known as combinatorics, the study of permutations – of how one can arrange particular groups of objects, numbers or letters according to stated laws. As early as 200 BC, writers on Sanskrit poetry asked how many ways it is possible to arrange various sets of long and short syllables, the building blocks of Sanskrit verse. A syllable is short, with one beat, or long, with two. In how many ways can a metre of four syllables be constructed? Four shorts or four longs have just one pattern for each, while for three shorts and a long, or three longs and a short, there are four (SSSL, SSLS, SLSS, and LSSS, for example). For two of each kind of syllable, there are six possibilities. Do the sum for metres of one, two, three, four and more and a mathematical pattern emerges. It is Pascal’s Triangle, the pyramid of numbers in which the series in the next line is given by adding together adjacent pairs in the line above to generate 1, 1 1, 1 2 1, 1 3 3 1, 1 4 6 4 1, and so on.As in a great poem, hidden within that elegant structure are deeper truths that touch on apparently unrelated things; on fractal patterns, on the theory of numbers, on primes, and of complexities too deep to be accessible to mere mortals untrained in the mathematical art.