किस बौद्ध ग्रंथ से यह ज्ञात होता है कि छठी शताब्दी ईसा पूर्व में 16 महाजनपद विद्यमान थे?

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?