7 (seven) is a positive integer following 6 and preceding 8. Its ordinal form is written "7th" or "seventh".
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.
Some googologisms based on 7 are googolseptiplex, supersept and trisept.
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.
The New Jersey metal band Symphony X composed and performed the song "Seven" as part of their album Paradise Lost.
Numbers named with the fuga- family of prefixes