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17 (number)

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17 (seventeen) is the natural number following 16 and preceding 18. In English, it is the smallest number with nine letters when spelled out.

Cardinal 17
seventeen
Ordinal 17th
seventeenth
Factorization prime
Divisors 1, 17
Roman numeral XVII
Binary 10001
Octal 21
Hexadecimal 11

In mathematics

Seventeen is the 7th prime number. The next prime is nineteen, with which it comprises a twin prime. 17 is the sum of the first four primes. 17 is the sixth Mersenne prime exponent, yielding 131071. 17 is an Eisenstein prime with no imaginary part and real part of the form [3n - 1].

17 is the third Fermat prime. Since 17 is a Fermat prime, heptadecagons can be drawn with compass and ruler. This was proved by Karl Friedrich Gauss. 17 is the second and last Genocchi prime. It is also the third Stern prime.

There are exactly seventeen two-dimensional space (plane symmetry) groups. These are sometimes called wallpaper groups, as they represent the seventeen possible symmetry types that can be used for wallpaper.

Like 41, the number 17 is a prime that yields primes in the polynomial n2 + n + p, for all positive n < p - 1.

Consider a sequence of real numbers between 0 and 1 such that the first two lie in different halves of this interval, the first three in different thirds, and so forth. The maximum possible length of such a sequence is 17 (Berlekamp & Graham, 1970, example 63).

16 and 18 unit squares can each be formed into rectangles with perimeter equal to the area; and they are the only solutions. The Platonists regarded this as a sign of their peculiar propriety; and Plutarch explains that 17 is therefore an unlucky number.

In base 9, the smallest prime with a composite sum of digits is 17.

17 is known as the Feller number, after the famous mathematician William Feller who taught at Princeton University for many years. Feller would say, when discussing an unsolved mathematical problem, that if it could be proved for the case n = 17 then it could be proved for all positive integers n. He would also say in lectures, "Let's try this for an arbitrary value of n, say n=17."

17! = 355687428096000

It is a repunit in hexadecimal.

It is believed that the minimum possible number of givens for a sudoku puzzle with a unique solution is 17, but this has yet to be proven.

In science

Astronomy

Age 17

In music

In other fields

Seventeen is:

Historical years

A.D. 17, 17 B.C., 1917, 2017, etc.

References

Berlekamp, E. R. and Graham, R. L., Irregularities in the distributions of finite sequences, J. Number Theory 2 (1970), 152–161.

External links

 


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