The Katapayadi Sutra is a system in Carnatic music (Indian classical) which allows one to find the 'number' of a raaga. The system only works with the Melakartha raagas, which are labeled from one through seventy-two. The number can then be used to find the exact notes of the scale (for example, whether the 4th note, equivalent of Western Fa, is high or low. The notes are defined only in relation to each other, not on a fixed scale like in Western music). The process is simple. The process is tied to the Indian alphabet Devanagari, though it will usually work pretty well no matter which Indian alphabet you use. One note: Devanagari is arranged in rows of 5 letters each.

For example, let's take Kamas raaga. The first sound is Ka, the first letter of the Indian alphabet (at least, counting consonants) and is thus the first in it's row. It is assigned the number 1. The second sound is Ma, which is a nasal, and is thus the fifth letter in its row. It is assigned a number of 5. Next, we switch the two numbers to get 51. This is the number for Kamas. We can tell a number of things from this number, for instance, that it has the 'high' Ma (mentioned earlier) because its number is greater than 36.

The Katapayadi Sutra is one of the most important parts of South Indian Classical Music. It is a very creative and efficient system that allows one to find a raaga simply by its name.

Note: This writeup assumes a basic knowledge of Indian Classical music, especially knowledge on what a raaga is. If you don't know what that is, check the writeup on it.