Where does “सइंत्रीस” come from?

सइंत्रीस (Middle Gujarati) comes from Sanskrit सप्तत्रिंशत्, from Sanskrit त्रिंशत्, from Proto-Indo-Aryan triHśát, from Proto-Indo-Iranian triHćát, from Proto-Indo-European tridḱómt, from Proto-Indo-European tri-, from Proto-Indo-European tréyes — three.

Ancestry of “सइंत्रीस”, step by step

Step	Language	Word	Meaning
1	Sanskrit	सप्तत्रिंशत्	thirty-seven
2	Sanskrit	त्रिंशत्	thirty
3	Proto-Indo-Aryan	triHśát	—
4	Proto-Indo-Iranian	triHćát	thirty
5	Proto-Indo-European	tridḱómt	thirty
6	Proto-Indo-European	tri-	three, threefold
7	Proto-Indo-European	tréyes	three

Words derived from “सइंत्रीस”

સાડત્રીસ

Every word from Proto-Indo-European tréyes →Every word from Proto-Indo-European tri- →Every word from Proto-Indo-European tridḱómt →