We have gone over the first two of six standard combinatorial techniques, *prastāraḥ* or “spreading out,” and *naṣṭaḥ* or “lost.” The third technique was developed to answer the following question. Suppose the sequence of light and heavy syllables in a given combination has been *indicated* (*uddiṣṭaḥ*). How can we find out the serial number of this particular combination in the *prastāraḥ* or “spreading out” of combinations?

The procedure is very simple:

- Start from the last
*light*syllable in the pattern, and start with*x*= 1. - For each syllable, going from right to left:
- If it is
**light**, multiply*x*by two, and use this as the new value of*x*for the next syllable. - If it is
**heavy**, multiply*x*by two, then subtract one, and use this as the new value of*x*for the next syllable. - The final value of
*x*is the serial number of the pattern.

Actually, one can start from the last *heavy* syllable in the pattern, too. But since the value of *x* passed onto the next syllable will inevitably be (1×2)-1 = 1, you might as well skip it.

For the pattern ।ऽ।ऽ (light-heavy-light-heavy), we can work out the serial number in the *prastāraḥ* of four-syllable patterns as follows:

**Fourth syllable**: heavy, so skip it.**Third syllable**: light, so we use 2*x*= 2×1 = 2.**Second syllable**: heavy, so we use 2*x*-1 = 2×2-1 = 3.**First syllable**: light, so we use 2*x*= 2×3 = 6.

Here it can be verified that ।ऽ।ऽ is the sixth pattern in the *prastāraḥ* of four-syllable patterns.

A more interesting problem would be to work out the serial number for well-known meters like the *vasantatilakam*. That is a 14-syllable meter, and hence there should be 2^{14} = 16,384 combinations. What is the serial number of the pattern ऽऽ।ऽ।।।ऽ।।ऽ।ऽऽ, that of the *vasantatilakam*? You can try to work it out yourself. The answer I came up with is 2,933.