Tuesday, December 8, 2009

425

425 = 52 x 17.

425 has three representations as a sum of two squares: 425 = 52 + 202 = 82 + 192 = 132 + 162.

425 is the hypotenuse of two primitive Pythagorean triples: 4252 = 872 + 4162 = 2972 + 3042.

425 is a pentagonal number, a number of the form n(3n - 1)/2, where n = 17.

425 is the number of subsets of {1, 2, 3, . . . 11} that have an integer average.

425 is the telephone area code for suburbs to the north and east of Seattle, Washington.

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