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## Summary

50 (fifty) is the natural number following 49 and preceding 51.

 ← 49 50 51 →
Cardinalfifty
Ordinal50th
(fiftieth)
Numeral systemquinquagesimal
Factorization2 × 52
Divisors1, 2, 5, 10, 25, 50
Greek numeralΝ´
Roman numeralL
Unicode symbol(s)
Binary1100102
Ternary12123
Octal628
Duodecimal4212

## In mathematics

Fifty is the smallest number that is the sum of two non-zero square numbers in two distinct ways: 50 = 12 + 72 = 52 + 52. It is also the sum of three squares, 50 = 32 + 42 + 52, and the sum of four squares, 50 = 62 + 32 + 22 + 12. It is a Harshad number.

50 is a Stirling number of the first kind: $\left[{5 \atop 2}\right]=50$ , and also a Narayana number: $\operatorname {N} (6,3)=\operatorname {N} (6,4)=50$

There is no solution to the equation φ(x) = 50, making 50 a nontotient. Nor is there a solution to the equation x − φ(x) = 50, making 50 a noncototient.

## In religion

• In Kabbalah, there are 50 Gates of Wisdom (or Understanding) and 50 Gates of Impurity[citation needed]
• The traditional number of years in a jubilee period.
• The Christian Feast of Pentecost takes place on the 50th day of the Easter Season
• The Jewish Pentecost takes place 50 days after the Passover feast (the holiday of Shavuoth).

## In other fields

Fifty is:

• There are 50 states in the United States of America.
• The TV show Hawaii Five-O and its reimagined version, Hawaii Five-0, are so called because Hawaii is the last (50th) of the states to officially become a state.
• 5-O (Five-Oh) - Slang for police officers and/or a warning that police are approaching. Derived from the television show Hawaii Five-O
• A calibre of ammunition (0.50 inches: see .50 BMG)
• In millimetres, the focal length of the normal lens in 35 mm photography
• The percentage (50%) equivalent to one half, so that the phrase "fifty-fifty" commonly expresses something divided equally in two; in business this is often denoted as being the ultimate in equal partnership
• In years of marriage, the gold or "golden" wedding anniversary
• The speed limit, in kilometres per hour, of Australian and Canadian roads with unspecified limits.