Seven (7) is a positive integer one more than 6 and one less than 8.


7 is the fourth prime number (between 5 and 11). It is a Mersenne prime exponent (producing 127), and is itself a Mersenne prime (between 3 and 31).

7 is the fourth Lucas number, coming between 4 and 11.

7 is in a twin prime pair with 5.

7 is widely considered a lucky number. It is also a lucky number in the numerical sense (between 3 and 9).

In googology Edit

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 sept- in Latin systems.

Donald Knuth calls this number septiad, and it's equal to using the -yllion system.


Using the gag prefix, seven can be called gagtwo, since A(2,2) = 7.

Seven is the smallest number of sides of a regular polygon that cannot be constructed with a compass and straightedge alone. 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.

In Culture Edit

The New Jersey metal band Symphony X composed and performed the song Seven as part of their album, Paradise Lost.