81 (number) facts for kids
Eighty-one is a special number that comes right after eighty and just before eighty-two. It's an odd number, which means you can't divide it evenly by two. Eighty-one is also a square number, which is pretty cool!
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What Makes 81 a Square Number?
A square number is what you get when you multiply a whole number by itself. For example, 2 multiplied by 2 is 4, so 4 is a square number. For 81, you get it by multiplying 9 by 9. So, 9 × 9 = 81. This means 81 is the ninth square number. Think of it like a square shape made of 81 small blocks, with 9 blocks on each side.
How Can We Find Square Numbers?
To find any square number, you just pick a whole number and multiply it by itself.
- 1 × 1 = 1
- 2 × 2 = 4
- 3 × 3 = 9
- 4 × 4 = 16
- 5 × 5 = 25
And so on! This pattern helps us understand why 81 is part of this special group of numbers.
Interesting Facts About the Number 81
The number 81 shows up in many different places, from math to everyday life. It has some unique properties that make it stand out.
Is 81 a Palindrome?
A palindrome is something that reads the same forwards and backwards. Think of words like "madam" or "level." The number 81 is not a palindrome because if you read it backwards, it becomes 18.
What About 81 in Other Number Systems?
Numbers can be written in different ways. In the octal (base-8) number system, 81 is written as 121. This is because 1 times 8 squared (64) plus 2 times 8 (16) plus 1 (1) equals 81. In the binary (base-2) system, which computers use, 81 is written as 1010001.
The Number 81 in Science and Culture
- In chemistry, 81 is the atomic number of the element Thallium. Thallium is a soft, gray metal. It's known for being quite toxic.
- In astronomy, there are many objects identified with the number 81. For example, Messier 81 (M81) is a beautiful spiral galaxy in the constellation Ursa Major. It's also known as Bode's Galaxy.
- In sports, 81 is a number often seen. For instance, in baseball, a regular season has 81 home games for each team.
- In music, some songs or albums might feature the number 81 in their titles or themes.
Math Fun with 81
The number 81 has some cool math tricks up its sleeve.
- It's the only number (besides 1) where the sum of its digits (8 + 1 = 9) is the square root of the number (the square root of 81 is 9).
- It's also a perfect power because it can be written as 3 to the power of 4 (3 × 3 × 3 × 3 = 81). This means it's not just 9 squared, but also 3 to the fourth power!
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