6 and preceding 8. Its ordinal form is written "7th" or "seventh".7 (seven) is a positive integer following
- 7 is an odd prime number. It is a Mersenne prime, since it is equal to 23-1.
- It is associated with good luck in Western culture.
- It is the third number in Sylvester's sequence.
- All Fermat numbers larger than 5 end in 7.
- In Greek-based number naming systems, 7 is associated with prefix hepta-, and with prefix septi- in Latin systems.
- Using the gag prefix, seven can be called gagtwo, since A(2,2) = 7.
- 7 is the last digit of Graham's number, and in fact it is the last digit of any power tower of 3's where the height of the tower is at least 2.
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