221 (number)

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← 220 221 222 →
Cardinaltwo hundred twenty-one
Ordinal221st
(two hundred twenty-first)
Factorization13 × 17
Greek numeralΣΚΑ´
Roman numeralCCXXI
Binary110111012
Ternary220123
Senary10056
Octal3358
Duodecimal16512
HexadecimalDD16

221 (two hundred [and] twenty-one) is the natural number following 220 and preceding 222.

In mathematics

221 is:

  • 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[1]
  • 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.

Historical years

References

  1. ^ "Sloane's A001844 : Centered square numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-26.
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