Here are a couple of interesting number facts:

**1. **In mathematics, a **congruent number** is a positive integer that is the area of a right triangle with three rational number sides. 6 is a congruent number because it is the area of a 3,4,5 triangle. The question of determining whether a given rational number is a congruent number is called the congruent number problem. This problem has not (as of 2012) been brought to a successful resolution.

**2. **In mathematics, the **Pell numbers** are an infinite sequence of integers, known since ancient times, that comprise the denominators of the closest rational approximations to the square root of 2. This sequence of approximations begins 1/1, 3/2, 7/5, 17/12, and 41/29, so the sequence of Pell numbers begins with 0, 1, 2, 5, 12, and 29 (each Pell number is the sum of twice the previous Pell number and the Pell number before that).

A Pell prime is a Pell number that is prime, such as 29.

Also, so those interested: Jan Brett (born December 1, 1949) is an American illustrator and writer of children’s picture books.

**3. **In recreational mathematics, a** Harshad number** (or Niven number) in a given number base, is an integer that is divisible by the sum of its digits when written in that base. Thus, you can observe that number 21 is indeed a Harshad number.

Moreover, Harshad numbers were defined by D. R. Kaprekar, a mathematician from India. The word “Harshad” comes from the Sanskrit harṣa (joy) + da (give), meaning joy-giver (so cute).

My promise to write number facts weekly didn’t work as planed and I am very sorry for this. I will try to redo my schedule and change a couple of things for the future. Thank you for your support.Hope you are all having fun this summer, don’t forget to check my Facebook event: Mathematics and Summer ^_^ Thank you for your help and support. Thank you for reading. You can find me on Facebook, Tumblr, Google+, Twitter, Instagram and Lettrs, I will try to post there as often as possible. *Don’t forget that maths is everywhere! Enjoy! *

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Thanks for sharing! I am using the congruent numbers for my pythagorean unit and the pell numbers for recursive functions.

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Thanks for this great information on the word “Harshad”! Some of Harshad numbers have some additional features, like for example 1729. If you are interested, read more here: http://www.glennwestmore.com.au/harshad-numbers/

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