The second President of the United States, John Adams, died on July 4, 1826, fifty years to the day the Declaration of Independence was signed. His last words, allegedly, were “Thomas Jefferson survives,” a homage to his former political rival and, by then, friend. Unbeknownst to Adams, Jefferson — the author of the Declaration and the nation’s third President — passed away earlier that same day.

Jefferson died having left at least one mystery unsolved. In 1801, while serving his first term as President, Jefferson received a letter from his friend and University of Pennsylvania professor Robert Patterson. Included in the message was the cipher — an encoded message — pictured above, which Patterson believed was “absolutely inscrutable” to anyone who did not know its key. To Jefferson, Patterson’s assertion probably felt correct, as there is no reason to believe the President (nor anyone else he knew) successfully decoded Patterson’s message.

Two centuries later, though, a Princeton-area code breaker (and Ph.D. in mathematics) proved Patterson wrong. Dr. Lawren Smithline, a former Cornell professor, broke the code in 2007, aided by a computer algorithm. (The computer, Smithline later suggested, was unnecessary — the number of sequences Patterson’s key used could have been narrowed down to roughly 100,000 combinations without the aide of a computer, and a code breaker could have checked all 100,000 possibilities by hand pretty easily, even in the 1800s, abject boredom notwithstanding.)

The message?

“In Congress, July Fourth, one thousand seven hundred and seventy six. A declaration by the Representatives of the United States of America in Congress assembled. When in the course of human events…” — roughly, the opening of the same Declaration originally penned by Jefferson himself.

Bonus fact : Ciphers may have been a hobby of Jefferson’s . The President was no stranger to learning new languages (albeit limited to real ones) — he apparently taught himself Arabic.

Related: The Taman Shud Mystery: A code which still needs cracking.