31. ithil muthaR patham praNavam.
Amongst the three parts of the Thirumanthra, the first part is praNavam.
Sri PBA Swami's Sarartha Deepikai:
Om which is the praNavam is the first part of the Thirumanthra. There are some who use "am" instead of "Om" to make up the Ashtakshara manthra. Perhaps to correct them, Sri Pillai Lokacharya is explicitly stating that the praNavam is the first part. The reason why he says praNavam instead of Om is because the manthra itself has to be received from an acharya through an upadesa.