72 (number) facts for kids

Seventy-two is an even number. It comes right after seventy-one and just before seventy-three. Seventy-two is a fascinating number with many interesting properties in mathematics and appears in various parts of our daily lives.

The Number 72

Seventy-two is a composite number, which means it can be divided evenly by more than just 1 and itself. It has quite a few divisors (numbers that divide into it without a remainder). These include 1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 36, and 72. Because it has so many divisors, 72 is considered a highly composite number.

Math Fun with 72

Seventy-two is a Harshad number (or Niven number) in base 10. This means it can be divided by the sum of its digits (7 + 2 = 9, and 72 divided by 9 is 8). It is also a pronic number because it is the product of two consecutive integers: 8 multiplied by 9 equals 72.

You can also think of 72 as a triangular number if you add up the numbers from 1 to 11 (1+2+3+...+11 = 66), but 72 itself is not a triangular number. However, it is related to triangular numbers in other ways. For example, 72 is the smallest number whose square (72x72 = 5184) is the product of three consecutive integers (16x17x18 = 4896, close but not quite).

Factors and Multiples of 72

Understanding factors and multiples helps us see how numbers relate to each other.

• Factors: The factors of 72 are 1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 36, 72.
• Multiples: The multiples of 72 are numbers you get by multiplying 72 by another whole number, like 72, 144, 216, 288, and so on.

Where You See 72

The number 72 appears in many interesting places, from science to everyday measurements.

In Time and Angles

• Hours in Days: There are 72 hours in three days (3 days x 24 hours/day = 72 hours).
• Degrees: In geometry, 72 degrees is a common angle. For example, a regular pentagon (a five-sided shape) has interior angles of 108 degrees, and its exterior angles are 72 degrees. A full circle is 360 degrees, and 72 is one-fifth of 360 (360 / 5 = 72).

In Science and Nature

• Human Body: A healthy adult's resting heart rate is often around 72 beats per minute.
• Astronomy: The "Rule of 72" is a quick way to estimate how long it will take for an investment to double, based on its annual interest rate. For example, if you earn 10% interest, it would take about 7.2 years (72/10) for your money to double.

In Sports and Games

• Golf: In golf, a par score for a standard 18-hole course is often 72. This means a professional golfer aims to complete the course in 72 strokes.
• Cards: In some card games, like certain versions of poker, 72 is a specific hand or score to aim for.