Sutra:
28. ithu thAn ettuth thiruvaksharamAy mUnRu pathamAy irukkum.

Meaning:
The Thirumathra is made up of eight aksharas (letters) and is of three parts.

Sri PBA Swami's Sarartha Deepikai:
This sutra shows the the number of aksharas and parts that make up the Thirumanthra. This will be followed by the explanations of the meanings of these letters and parts.

Some people break up the Thirumathra as follows. They break the nArAyaNAya as "nAra ayanAya" which then becomes six aksharas. Then, they drop the praNavam in order to derive the eight aksharas. However, as this contradicts the sruthi "OmityekAksharam; nama iti dve akshare; nArAyaNAyeti panjcAksharANi", such break up is not considered appropriate.