Googology Wiki
Googology Wiki

72 (seventy-two) is a positive integer following 71 and preceding 73. Its ordinal form is written "seventy-second" or 72nd.


72 is an even composite number.

Rule of 72[1] is a method for estimating the time required for a given principal to double. It is calculated as t = ln 2 / (ln(1+r)) and can be approximated as \(t \approx 0.72/r\). It is especially used in finance to estimate an investment's doubling time. For example, when the rate is 6%, 0.72/0.06 = 72/6 = 12 years is required to double the investiment, where the actual value is about 11.896.

In googology

In Greek-based number-naming systems, 72 is associated with prefix "duheptaconta-", and with prefix "duoseptuaginti-" in Latin systems.

In shogi

It is also the number of possible pawn moves (by a given player) in shogi.

In TV broadcasting

In the Americas, the mid gap in the Band I starts at 72 MHz.


  1. MathWorld, Rule of 72