Thursday, October 7, 2010

820

820 = 22 x 5 x 41.

820 has two representations as a sum of two squares: 820 = 62 + 282 = 122 + 262.

820 is the 40th triangular number.

820 is a divisor of 812 - 1.

810 is 1111 in base 9.

Muhammad ibn Musa al-Khwarizmi presented the first systematic solution of linear and quadratic equations in the year 820 in The Compendious Book on Calculation by Completion and Balancing.

Source: WolframAlpha
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