This handout photo released by courtesy of RR Auction shows a handwritten letter from Albert Einstein to Polish-U.S. physicist Ludwik Silberstein, dated October 26, 1946, in which Einstein wrote out the equation "E = mc2" (top R) in German. The letter was sold for $1,243,707 during the auction from May 13 to 20, 2021. (Photos: Agencies)

This handout photo released by courtesy of RR Auction shows a handwritten letter from Albert Einstein to Polish-U.S. physicist Ludwik Silberstein, dated October 26, 1946, in which Einstein wrote out the equation "E = mc2" (top R) in German. The letter was sold for $1,243,707 during the auction from May 13 to 20, 2021.

This handout photo released by courtesy of RR Auction shows a handwritten letter from Albert Einstein to Polish-U.S. physicist Ludwik Silberstein, dated October 26, 1946, in which Einstein wrote out the equation "E = mc2" (top R) in German. The letter was sold for $1,243,707 during the auction from May 13 to 20, 2021.