Which mathematical concept was the central theme of Casio's award-winning 2014 calculator marketing campaign that went viral among mathematics students and educators?

The intersection of mathematics and retail marketing has led to revolutionary approaches in customer targeting and engagement. Mathematical models power modern retail strategies, from predictive analytics to algorithmic pricing. This trivia tests your knowledge of how a famous mathematical concept was brilliantly leveraged in a retail marketing campaign that became legendary in both the mathematics and marketing communities.

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The Golden Ratio (φ), with their 'Perfectly Proportioned Calculations' campaign showing how their calculator design incorporated the 1.618... ratio
Euler's Identity (e^(iπ)+1=0), with their 'Beauty in One Button' campaign demonstrating how their scientific calculator could compute this elegant equation efficiently
The Fibonacci Sequence, with their 'Nature's Pattern, Your Success' campaign linking the mathematical sequence to progressive learning outcomes
Fermat's Last Theorem, with their 'Some Equations Take Centuries, Yours Take Seconds' campaign highlighting the calculator's advanced equation-solving capabilities