101 number
101 (one hundred [and] one) is the natural number following 100 and preceding 102.
Template:Numbers 100s | |
Cardinal | one hundred [and] one |
Ordinal | 101st (one hundred [and] first) |
Factorization | prime |
Roman numeral | CI |
Binary | 1100101 |
Hexadecimal | 65 |
Hebrew | קא (Qof Alef) |
In mathematics
101 is the 26th prime number and a palindromic number (therefore also a palindromic prime). The next prime is 103, with which it comprises a twin prime (making 101 a Chen prime). Because the period length of its reciprocal is unique among primes, 101 is a unique prime. 101 is an Eisenstein prime with no imaginary part and real part of the form .
101 is the sum of five consecutive primes (13 + 17 + 19 + 23 + 29). Given 101, the Mertens function returns 0.
101 is a centered decagonal number.
For a 3-digit number in base 10, this number has a relatively simple divisibility test. The number is split into groups of four, starting with the rightmost four, and added up to produce a 4-digit number. If this 4-digit number is of the form 1000a + 100b + 10a + b (where a and b are integers from 0 to 9), such as 3232 or 9797, or of the form 100b + b, such as 707 and 808, then the number is divisible by 101. This might not be as simple as the divisibility tests for numbers like 3 and 5, and it might not be terribly practical, but it is simpler than the divisibility tests for other 3-digit numbers.
In astronomy
- The Messier object M101, a magnitude 8.5 spiral galaxy in the constellation Ursa Major, also known as the Pinwheel Galaxy
- The New General Catalogue object NGC101, a magnitude 12.9 spiral galaxy in the constellation Sculptor
- The Asteroid 101 Helena.
In other fields
101 is also:
- The atomic number of mendelevium, an actinide.
- The designation of US Highway 101, which runs from California to Washington.
- In universities of the United States, sometimes the course number of basic or entry-level courses. Also used in titles of books to indicate the book is meant for a beginner. At universities with four-digit course numbers, the equivalent course number is 1001 or 1010. This usage is now becomming common parlence in business-speak where it is pronounced "one oh one".
- In the title of the book The Hundred and One Dalmatians by Dodie Smith (and the various movie versions thereof).
- The number of keys on a standard PC alphanumeric keyboard, including 12 or so function keys, cursor keys, and a numeric keypads and various other additions to the QWERTY typewriter keyboard.
- According to Books in Print, more books are now published with a title that begins with '101' than '100'. They usually describe or discuss a list of items, such as 101 ways to ... or 101 questions and answers about .... This marketing tool is used to imply that the customer is given a little extra information beyond books that include only 100 items. Some books have taken this marketing scheme even further with titles that begin with '102', '103', or '1001'.
- Room 101 in George Orwell's novel Nineteen Eighty-Four
- Unit 101 of the Israeli Defense Forces.
- 101st_Airborne_Division of the United States Army
- A live album by Depeche Mode.
- The year AD 101 or 101 BC.
See also: 101st km
es:Ciento uno fr:101 (nombre) ko:101 it:Centouno ja:101 ru:101 (число) sl:101 (število) sv:101 (tal) zh:101