A letter containing the equation E = mc², written by Albert Einstein, sold for $ 1.2 million (or R $ 6.4 million) at an auction in the United States, more than tripled.

Experts say there are only three other known examples of the equation in the physicist’s handwriting.

The auctioned letter is the only example of the equation in a private collection, and the RR auction in Boston, USA, which recently sold the letter saying it was public.

This equation was first published by Einstein in a scientific article in 1905, establishing the equivalence of matter and energy. Equation is the basic concept of modern physics (light energy is twice the mass of the square of the light square).

“This is an important card from a holographic, physical point of view,” RR Auction said in a statement, “the most well-known equation ever established.”

A one-page letter in German was sent on October 26, 1946, addressing the Polish-American physicist Ludwig Silberstein, who opposed some of Einstein’s theories.

The letter was part of Silberstein’s personal files and was sold by his successors, the Associated Press news agency reported, only to identify the buyer as an anonymous document collector.