After studying the numbers, it is easy to understand the first and second form of numbers. So let us begin.
These numbers are used as adjectives and can be also used in a sentence to name a chapter, for instance;
अथ प्रथमो ऽध्यायः । अर्जुनविषादयोगः
atha prathamo ‘dhyāyaḥ । arjuna-viṣāda-yogaḥ
Now starts the first chapter: the yoga of Arjuna’s despair
One thing to note is, just as English uses the sound –th from Four, similarly in Sanskrit, the –I sound is used for the feminine.
11th to 19th
The numbers are almost same, and can be formed by inflicting like the noun ending –a. for feminine its –i
अथ षोडशो ऽध्यायः । दैवासुरसम्पद्विभागयोगः
atha ṣoḍaśo ‘dhyāyaḥ । daiva-asura-sampad-vibhāga-yogaḥ
Now starts the sixteenth chapter: the yoga of the division between divine and demonic fates
20TH to 99th
To get the form, ‘tama’ is added to the end of the word, it can also be contracted to a shorter form.
एकविंश, चतुस्त्रिंश, नवचत्वारिंश, अष्टापञ्चाश, द्वाषष्ट, सप्तसप्तत, पञ्चाशीत, षड्णवत
ekaviṃśa, catustriṃśa, navacatvāriṃśa, aṣṭāpañcāśa, dvāṣaṣṭa, saptasaptata, pañcāśīta, ṣaḍṇavata
Twenty-first, thirty-fourth, forty-ninth, fifty-eighth, sixty-second, seventy-seventh, eighty-fifth, Ninety-sixth
Either ‘tama’ is added or it is same.