In the strong cases with the exception of Vocative Case singular, the penultimate vowel is lengthened in the case of a aṅga (stem) ending in s with a Nasal consonant preceding it, and of mahat,
That is, a stem ending in the conjunct consonant न्स्, elongates its penultimate vowel before the affixes of the first five cases. Thus श्रेयान्, श्रेयांसौ, श्रेयांसः, श्रेयांसि, पयांसि, यशांसि ॥ महत्-महान्, महान्तौ, महान्तः ॥ But हे श्रेयन्, हे महन् in Vocative Singular. The Nasal is inserted by 7.1.70.,