Handwritten Example of Famous Einstein Equation Gets $1.2 Million

In this undated photograph, provided by Boston-based RR Auction, shows a letter written by Albert Einstein, in which he wrote out his famous "E = mc2" equation, that sold at auction for more than $1.2 million. Archivists at the Einstein Papers Project at the California Institute of Technology and the Hebrew University of Jerusalem say there are only three other known examples of Einstein writing the world-changing equation in his own hand. Nikki Brickett/RR Auction via AP

BOSTON—A letter written by Albert Einstein in which he writes out his famous E = mc2 equation has sold at auction for more than $1.2 million, about three times more than it was expected to get, Boston-based RR Auction said Friday.

Archivists at the Einstein Papers Project at the California Institute of Technology and the Hebrew University of Jerusalem say there are only three other known examples of Einstein writing the famous equation in his own hand.