7 (number) facts for kids

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Cardinal	seven
Ordinal	7th (seventh)
Numeral system	septenary
Factorization	prime
Prime	4th
Divisors	1, 7
Greek numeral	Ζ´
Roman numeral	VII
Roman numeral (unicode)	Ⅶ, ⅶ
Greek prefix	hepta-/hept-
Latin prefix	septua-
Binary	1112
Ternary	213
Senary	116
Octal	78
Duodecimal	712
Hexadecimal	716
Greek numeral	Z, ζ
Amharic	፯
Arabic	٧,7
Persian	٧ - هفت
Urdu
Bengali	৭
Chinese numeral	七(qi)
Devanāgarī	७ (saat)
Telugu	౭
Tamil	௭
Hebrew	ז (Zayin)
Khmer	៧
Thai	๗

The number seven is a natural number. It comes right after six and just before eight. In Roman numerals, we write it as VII. Seven is a very interesting number that appears in many places, from math to nature and even in stories.

Seven in Math

In mathematics, the number seven is special. It is an odd number, meaning you can't divide it evenly by two. Seven is also a prime number. A prime number is a whole number greater than 1 that has only two divisors: 1 and itself. So, 7 can only be divided by 1 and 7 without leaving a remainder.

Seven is also a Mersenne prime. This is a special type of prime number that can be written as 2^p - 1, where 'p' is also a prime number. For seven, p is 3, because 2³ - 1 = 8 - 1 = 7.

How to Check if a Number Can Be Divided by 7

There's a cool trick to see if a big number can be divided by 7. It's called the divisibility rule for 7. Here's how it works:

1. Take the last digit of the number and multiply it by 2.
2. Subtract this result from the rest of the number (the number without its last digit).
3. Keep repeating these steps. If your final number can be divided by 7, then the original big number can also be divided by 7!

Example Let's try with the number 918785:

1. The last digit is 5. Multiply 5 by 2: 5 × 2 = 10.
2. The rest of the number is 91878. Subtract 10 from it: 91878 - 10 = 91868.
3. Now, take 91868. The last digit is 8. Multiply 8 by 2: 8 × 2 = 16.
4. The rest of the number is 9186. Subtract 16 from it: 9186 - 16 = 9170.
5. Next, take 9170. The last digit is 0. Multiply 0 by 2: 0 × 2 = 0.
6. The rest of the number is 917. Subtract 0 from it: 917 - 0 = 917.
7. Finally, take 917. The last digit is 7. Multiply 7 by 2: 7 × 2 = 14.
8. The rest of the number is 91. Subtract 14 from it: 91 - 14 = 77.

Since 77 can be divided by 7 (77 ÷ 7 = 11), the original number 918785 can also be divided by 7!

Seven in Our World

The number seven pops up in many interesting places around us:

• There are seven beautiful colors in a rainbow: red, orange, yellow, green, blue, indigo, and violet.
• The element nitrogen has an atomic number of 7. This means each nitrogen atom has 7 protons in its center.
• The periodic table of elements has seven horizontal rows, which are called periods.
• There are seven days in a week: Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, and Sunday.
• People often talk about the "seven seas" and the "seven continents" of the world.
• Some beliefs mention "seven gates of heaven." For example, in the Quran (chapter 15, verse 44), it talks about seven gates.
• The human body can be thought of as having seven major parts: two legs, two hands, the main body (trunk), the neck, and the head.

Images for kids

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  A friendly robot, ready to learn about numbers!