Da Vinci Quest on Google – Day 23

I am stuck on Day 23 of the Da Vinci Quest on Google. After completing the puzzle, you are asked what city you are looking at. This one is easy: Paris!

Now you need to find 9 symbols on the map.

The symbols together outline a chalice, and the clue is this:

You have found all nine Cinquefoil icons! The icons reveal a hidden Chalice, centering on La Pyramide Inversee. But from above, it looks like something completely different; something related to the number of icons you have discovered on each Geography Challenge: 0, 1, 4, 9, … what is this classical squence?

Now, I’ve tried all the obvious answers:
Sequence of sqaures
Sequence of perfect squares
Palindromic perfect squares
Smarandache sequence
None of these work!

Anyone have ideas?

UPDATE: The answer was simply “square“. Go figure.