221 (two hundred [and] twenty-one) is the natural number following 220 and preceding 222.
| ||||
|---|---|---|---|---|
| Cardinal | two hundred twenty-one | |||
| Ordinal | 221st (two hundred twenty-first) | |||
| Factorization | 13 × 17 | |||
| Divisors | 1, 13, 17, 221 | |||
| Greek numeral | ΣΚΑ´ | |||
| Roman numeral | CCXXI, ccxxi | |||
| Binary | 110111012 | |||
| Ternary | 220123 | |||
| Senary | 10056 | |||
| Octal | 3358 | |||
| Duodecimal | 16512 | |||
| Hexadecimal | DD16 | |||
In mathematics
editIts factorization as 13 × 17 makes 221 the product of two consecutive prime numbers, the sixth smallest such product.[1]
221 is a centered square number,[2] an Ulam number,[3] and a brilliant number,[4] meaning that its prime factors have the same amount of digits.
In other fields
editThe year 221 BC marked the end of the Warring States period and the beginning of the Qin dynasty in China.[5]
221b Baker Street is the address of the fictional detective Sherlock Holmes, created by Sir Arthur Conan Doyle.[6]
References
edit- ↑ Sloane, N. J. A. (ed.). "Sequence A006094 (Products of 2 successive primes)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
- ↑ Sloane, N. J. A. (ed.). "Sequence A001844 (Centered square numbers)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
- ↑ Sloane, N. J. A. (ed.). "Sequence A002858 (Ulam numbers)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
- ↑ Sloane, N. J. A. (ed.). "Sequence A078972 (Brilliant numbers)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
- ↑ "Qin Dynasty". Smithsonian Institution. Retrieved 15 April 2025.
- ↑ "221B Baker Street". Sherlock Holmes Museum. Retrieved 2025-04-15.
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