181 (number)
Encyclopedia : 1 : 18 : 181 : 181 (number)
181 is the natural number between 180 and 182.
| |||
| Ordinal | One hundred [and] eighty-one | ||
| Cardinal | 181st | ||
| Factorization | prime number | ||
| Roman numeral | CLXXXI | ||
| Binary | 10110101 | ||
| Hexadecimal | B5 | ||
In mathematics
181 is a prime number, and a twin prime with 179, making 181 a Chen prime. In base 10, it is a palindromic prime.
181 is not a regular polygonal number in any way besides being 181-gonal, but it is a centered number in three different ways: it is a centered square number, centered pentagonal number and a star number.
181 is the sum of two consecutive squares and the sum of five consecutive primes (29 + 31 + 37 + 41 + 43).
181 is the rider number given to Lance Armstrong in 1999 when he won his first of seven Tour de France victories consecutively. After winning his first he returned to each subsequent tour as rider number 1 which is traditionally given to the previous years' defending overall winner.
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