# Seven

Six fears it, nine is it's food: seven.

## Properties

Seven is a mersenne prime: (2^3)-1 = 7. It's perfect number is 28 = (2^2)(7). It's a safe prime, as (2^((2^2)-1)-1 = 7.

7 is the sum of 8's proper divisors: 1+2+4.

7! = 7*6*5*4*3*2*1 = 5040, the last superior highly composite factorial.

### For different bases

- In binary, 7 is 111, a repunit!
- In ternary, 7 is 21.
- In quaternary, 7 is 13.
- In quinary, 7 is 12.
- In seximal, 7 is 11.
- In septimal, 7 is 10.
- In higher bases, 7.
- In negabinary, 7 is 11011

and -7 is 1001.
- In negaternary, 7 is 111

and -7 is 1202.
- In negaquaternary, 7 is 133

and -7 is 21.
- In negaquinary, 7 is 143

and -7 is 23.
- In negaseximal, 7 is 152

and -7 is 25.
- In negaseptimal, 7 is 160

and -7 is 10.

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