By Marc KaufmanWashington Post Staff Writer
Who would turn down a $1 million prize for solving a math problem?
Perhaps the smartest man in the world.
Three months ago, a famously impoverished Russian mathematician named Grigori Perelman was awarded the prestigious $1 million Clay Mathematics Institute Millennium Prize for his groundbreaking work -- having solved a problem of three-dimensional geometry that had resisted scores of brilliant mathematicians since 1904.Thursday, the institute announced that Perelman, known equally for his brilliance and his eccentricities, formally and finally turned down the award and the money. He didn't deserve it, he told a Russian news service, because he was following a mathematical path set by another...........