The first computer program was written a century before there was a computer to run it

In 1843, Ada Lovelace translated an Italian paper on Charles Babbage's unbuilt Analytical Engine and added her own notes, three times longer than the original — including a detailed algorithm for calculating Bernoulli numbers. Historians consider it the first published computer program, written for a machine made of gears that never got fully built in her lifetime.

— Ada Lovelace, Notes on L. F. Menabrea's 'Sketch of the Analytical Engine' — 1843 — public domain