(CNN)A letter written by Albert Einstein that includes the world’s most famous equation is being auctioned with an estimated worth of $400,000
The letter, written by Einstein to the Polish-American physicist Ludwik Silberstein, was penned in 1946 and contains the only handwritten example of “E=mc2” in private possession, according to a news release from RR Auction.
Archivists at the Einstein Papers Project at Caltech and the Hebrew University of Jerusalem say the papers that reside at the schools contain the only other known holographic examples.