शून्य की अवधारणा को सबसे पहले किस प्राचीन भारतीय गणितज्ञ द्वारा स्पष्ट रूप से परिभाषित किया गया था?

In Ancient Indian Statecraft, Kautilya's 'Rajamandala' theory primarily deals with:

The First Buddhist Council was held at ______.

Which ancient Indian text contains references indicating that population counts or census-like records were maintained in ancient India?