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|---|---|---|---|---|
| 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 | |||
221 (two hundred [and] twenty-one) is the natural number following 220 and preceding 222.
In mathematics
[edit]Its 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
[edit]The 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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