## Sunday, October 11, 2015

### 10 Math/Number Facts (Vol. #3)

1. The rule of 72 : It is used as an approximation in banking and finance for the time it took an investment to double at r%. For a 10% return on investment, the approximate period would be 72/10 = 7.2 years. The rule applies to compound interest.

2. In English, the name of every odd number contains the letter E.

3. An illegal prime is a prime number that represents information whose possession or distribution is forbidden in some legal jurisdiction. One of the first illegal primes was found in 2001. When interpreted in a particular way, it describes a computer program that bypasses the digital rights management scheme used on DVDs. Distribution of such a program in the United States is illegal under the Digital Millennium Copyright Act.

4. A US company called Fractal Antenna Systems, Inc. makes antenna arrays that use fractal shapes to get superior performance characteristics, because they can be packed so close together.

This design ensures performance improvements in antennae used in wireless, microwave, RFID (Radio Frequency Identification) and telecommunications.

5. In 1796, according to an unfounded legend, the metric system was born. The Oct 10 (10/10) date seems to signify the base 10 way of using measurements. A real birth date might be 8 May 1790, when acting on a motion by a bishop, Charles Maurice de Talleyrand (1754-1838), the French National Assembly decided to create a simple, stable, decimal system of measurement units. The earliest metre unit chosen was the length of a pendulum with a half-period of a second.

6. For Pythagoras, 10 was the symbol of the universe and all human knowledge.

7. Ahmes, an Egyptian scribe, is the earliest contributor to math whose name is known. He wrote the Rhind Mathematical Papyrus, a work of Ancient Egyptian mathematics that dates to approximately 1650 BC.

8. 19 is the only prime equal to the difference of two cubed primes.
19 = 3^3 - 2^3.

9. The sum of the reciprocals of the Fibonacci numbers is: 3.3598856662431775531720113029....

10. 284 is an amicable (or friendly) number paired with 220. The divisors of 220 add up to 284 and the divisors of 284 add up to 220. Amicable numbers were known to the Pythagoreans, who credited them with many mystical properties. A general formula by which some of these numbers could be derived was invented circa 850 by Thābit ibn Qurra (826-901).

Also have a look at : Vol#2 and Vol#1