James Abram Garfield was the 20th President of the United States of America. While not a mathematician he is included here because in 1876 while a Congressman he was credited with finding an original proof of the Pythagorean Theorem. The proof is interesting in that unlike many proofs his proof did not use the squares of sides of a triangle, instead it uses a pair of identical triangles of sides a, b, and c along with an isosceles triangle with legs of length c to create a trapezoid.
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Currency
First Day Covers
Stamp  Description 

United States, 6c, 1926 Scott: 638 A161 

United States, 20c, 1938 Scott: 825 A297 