221 (number)

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

• 221 A.D. and 221 B.C.

References