किस मगध शासक को 'सेनीय' के नाम से जाना जाता था, जिसका अर्थ है एक बड़ी और नियमित स्थायी सेना रखने वाला?

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?