Which mathematical constant has been used by some specialty bookstores and educational retailers to create a 'premium pricing' strategy, where products are priced at multiples of this number to convey mathematical elegance?

In recent years, some innovative retailers have turned to mathematics to optimize their pricing strategies. One particularly interesting approach involves the use of mathematical constants and principles to create psychologically appealing price points. This poll tests your knowledge about the intersection of mathematical concepts and retail pricing strategies that have gained popularity in specialty markets.

This is a live public trivia poll on AIPolls.Net. Vote and see real-time results.

Pi (3.14159...)
The Golden Ratio (1.61803...)
Euler's Number (2.71828...)
The Square Root of 2 (1.41421...)