Sunday, June 21, 2015

Special properties of number 21 (Today’s Date)

1. Twenty-one is a Fibonacci number, a Harshad number, triangular number and an octagonal number, as well as a composite number, its proper divisors being 1, 3 and 7.
2. 21 is the sum of the first six natural numbers (1+2+3+4+5+6=21), making it a triangular number. Also, the number of spots on a standard cubical (six-sided) die (1+2+3+4+5+6)
3. 21 is the smallest non-trivial example of a Fibonacci number whose digits are Fibonacci numbers and whose digit sum is also a Fibonacci number.
4. 21 is a repdigit in base 4 (1114).
5. 21 is the third star number. Star numbers can be represented by a square with a triangle on each side.
6. 221 - 21 is prime.
7. The current century—spanning the years from 2001 to 2100—is referred to as the 21st century.
8. 21 grams is the weight of the soul, according to research by Duncan MacDougall, generally regarded as meaningless.
9. The Chemical Element Scandium has an atomic number of 21.
10. There are 21 letters in the Italian alphabet.

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