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|Cardinal||two hundred twenty-one|
(two hundred and twenty-first)
|Factorization||13 × 17|
- a product of two prime numbers, 13 and 17, making it a semiprime
- the sum of five consecutive prime numbers (37 + 41 + 43 + 47 + 53)
- the sum of nine consecutive prime numbers (11 + 13 + 17 + 19 + 23 + 29 + 31 + 37 + 41)
- a centered square number
- Mertens function(221) = 5 a record high that stands until 554
- If you deal 2 cards from a single deck of 52 cards, you have a 1 in 221 chance of getting 2 aces.
In other fields
- SMTP status code for service closing transmission channel
- 221B Baker Street, the fictional London residence of Sherlock Holmes
- The experiment number for Sparky in the Disney franchise Lilo & Stitch.
- .221 Remington Fireball, firearm cartridge
- "Sloane's A001844 : Centered square numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-26.
- Conan Doyle, Sir Arthur A Study in Scarlet pub. Wordsworth Editions Limited (2004) p.10 "We met next day, as [Holmes] had arranged, and inspected the rooms at No. 221B Baker Street, of which he had spoken at our meeting." ISBN 978-1-84022-411-5