The augment (num) n is added in the strong cases to a Neuter aṅga (stem) ending in a consonant (other than a nasal or a semi-vowel) or ending in a vowel.,
Thus उदश्विन्ति, शकृन्ति 6.4.10 यशांसि, पयांसि; कुण्डानि, वनानि 6.4.8, त्रपूणि, जतूनि ॥ Why 'of a Neuter'? Observe अग्निचिद् ब्राह्मणः ॥ Why do we say 'not ending in a semivowel or a nasal'? Observe बहुपुरि, बहुधुरि, विमलदिवि, चत्वारि, अहानि (VII. I. 98). A neuter having an indicatory उक् vowel gets नुम् by this sutra and not by (VII. I. 70), as that is superseded by this, this being the subsequent. As श्रेयांसि, भूयांसि कुर्वन्ति कृषन्ति ब्राह्मणकुलानि ॥
Vart:- Prohibition should be stated with regard to बहूर्जि; as बहूर्जि ब्राह्मणकुलानि ॥ Some would have न् added between र् and ज् of this word, as बहूर्ञ्जि ब्राह्मणकुलानि ॥ See 1.4.13.,