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* '''19''' - was the average age of front-line [[US]] service personnel fighting to defend democracy in [[Indochina]] during the [[Vietnam War]].

* '''19''' - was the average age of front-line [[US]] service personnel fighting to defend democracy in [[Indochina]] during the [[Vietnam War]].

* '''19''' - [[Evariste Galois]] develops [[group theory]], and wrote it out completely on the eve of his death at age 20; it took old [[mathematicians]] a century to comprehend it.

* '''19''' - [[Evariste Galois]] develops [[group theory]], and wrote it out completely on the eve of his death at age 20; it took old [[mathematicians]] a century to comprehend it.

* '''19'''- [[John D. Rockefeller]] started his company, turning an enormous profit in its first year, and became the most influential businessman in history.<ref>http://www.notablebiographies.com/Pu-Ro/Rockefeller-John-D.html</ref>

* '''19'''- [[John D. Rockefeller]] starts a new company, turning an enormous profit in its first year, and became the most influential businessman in history.<ref>http://www.notablebiographies.com/Pu-Ro/Rockefeller-John-D.html</ref>

* '''20''' - Carl Friedrich Gauss makes his first mathematical discoveries, which will lead to the completion of "Disquisitiones Arithmeticae", his magnum opus, at the age of 21.

* '''20''' - Carl Friedrich Gauss makes his first mathematical discoveries, which will lead to the completion of "Disquisitiones Arithmeticae", his magnum opus, at the age of 21.