He felt himself suddenly reeling back to Harvard, standing in front of his "Symbolism in Art" class, writing his favorite number on the chalkboard.

1.618

Langdon turned to face his sea of eager students. "Who can tell me what this number is?"

A long-legged math major in back raised his hand. "That's the number PHI." He pronounced it fee.

"Nice job, Stettner," Langdon said. "Everyone, meet PHI."

"Not to be confused with PI," Stettner added, grinning. "As we mathematicians like to say: PHI is one H of a lot cooler than PI!"

Langdon laughed, but nobody else seemed to get the joke.

Stettner slumped.

"This number PHI," Langdon continued, "one-point-six-one-eight, is a very important number in art. Who can tell me why?"

Stettner tried to redeem himself. "Because it's so pretty?"

Everyone laughed.

"Actually," Langdon said, "Stettner's right again. PHI is generally considered the most beautiful number in the universe."

The laughter abruptly stopped, and Stettner gloated