## Friday, July 9, 2010

### 821

821 is a prime number.

821 has a representation as a sum of two squares: 821 = 142 + 252.

821 and 823 form a twin prime pair.

821 is the hypotenuse of a primitive Pythagorean triple: 8212 = 4292 + 7002.

821 is the maximum number of regions into which 40 lines divide the plane.

821 is the smallest prime whose reversal is a seventh power: 128 = 27.

821 = 6! + 5! - 4! + 3! - 2! + 1!

Aeroflot Flight 821 crashed on approach to Perm airport on Sept. 14, 2008.

#### 1 comment:

Anonymous said...

Otras representaciones de 821
821 es una terna pitagorica primitiva ya que
(821^2)^2=305959^2+600600^2
821=9^2+16^2+22^2=14^2+15^2+20^2
821^5=277030821^2-27635610^2
821 es el principal primo de cuatro consecutivos de la forma
p,p+2,p+6 y p+8 {821,823,827,829}
ver http://primes.edu/glosary
821 admite factorizaciĆ³n gaussiana en la forma
821=(25+14i)(14+25i)(-i)
821 tiene representaciĆ³n en los campos cuadraticos reales
821=29^2-5*2^2
821=37^2-137*2^2
821=43^2-257*2^2
821=47^2-347*2^2
y en los campos cuadraticos imaginarios
821=3^2+203*2^2
821=5^2+199*2^2
821=7^2+193*2^2
821=11^2+7*10^2
821:ISBN-0-821 es el International Standard Book Number para los libros publicados por la American Mathematical Society ver