The holiday is observed on March 14 or 3/14 because 3.14 are the first three digits of the infinite number pi — 3.14159 ... and on and on. The celebration of Pi Day was the brainchild of physicist Larry Shaw and was first observed in 1988 at San Francisco’s Exploratorium,

The man last known to be seen with a University of Pittsburgh student before she vanished from a beach in the Dominican Republic gave more details to local prosecutors about the last time he saw her,

From schoolkids learning about constant numbers to pizza deals to school serious math equations, here’s a slice of Pi Day fun.