221 (number)

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

← 220 221 222 →
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Cardinal	two hundred twenty-one
Ordinal	221st (two hundred twenty-first)
Factorization	13 × 17
Greek numeral	ΣΚΑ´
Roman numeral	CCXXI
Binary	110111012
Ternary	220123
Octal	3358
Duodecimal	16512
Hexadecimal	DD16

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

• 221 A.D. and 221 B.C.

References

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