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First, you want to know the definition of a perfect number:
A perfect number is an integer which is equal to the sum of all its positive integer divisors that are less than itself.
Example: The positive integer divisors of 6, less than 6, are 1, 2, and 3. The sum of those divisors is 1 + 2 + 3 = 6. Therefore, 6 is a perfect number.
Now, 21 does not meet this definition and therefore is not a perfect number.
Let's try it. There are three positive divisors of 21, namely, 1, 3, and 7, that are less than 21, itself. (There are no others.) But the sum of these divisors is
1 + 3 + 7 = 11, which is not equal to 21. Therefore, we confirm that 21 is not a perfect number.
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What is a mirror perfect number?
A perfect number is equal to the sum of its proper positive divisors.A mirror perfect number is equal to the sum of its proper positive divisors when they are read backwards.From a paper by Joseph L. Pe which is available on the 'net:10311 = 1 + 3 + 7 + 21 + 491 + 1473 + 34377343 + 3741 + 194 + 12 + 7 + 3 + 1 = 1130110311 is perfect and mirror perfect.
What is the sum of the first perfect number and the second perfect number?
The sum of the 1st perfect number and 2nd perfect number is. . . 34!
Can a perfect number be odd?
If by 'perfect number' you mean 'perfect SQUARE', then yes. 49 is an odd number and a perfect square.
What two square numbers total 21?
There is no pair of perfect squares that sums to 21. And the question is pointless if it is not about perfect squares because in that case there are infinitely many answers.There is no pair of perfect squares that sums to 21. And the question is pointless if it is not about perfect squares because in that case there are infinitely many answers.There is no pair of perfect squares that sums to 21. And the question is pointless if it is not about perfect squares because in that case there are infinitely many answers.There is no pair of perfect squares that sums to 21. And the question is pointless if it is not about perfect squares because in that case there are infinitely many answers.
Is 73 the perfect number?
73 is not a Perfect number.
What is the least number to be added to 1500 to make it a perfect square?
21
Is 21 a perfert square?
Square Number: A number that is a product of some integer with itself. Therefore, 21 is not a perfect square. An example of a perfect square is 16, since 4 times 4 is 16.
Is 21 a perfect number?
sorry mans it's not but on the bright side 28 is :)
Is 21 perfect?
The definition of perfect number is a number x such that its factors, excluding itself, when summed up form a total of x.An example of it is 6:Its factors (excluding itself) are 1,2 and 31+2+3=6AmazingAnother is 28:Factors excluding itself: 1,2,4,7 and 141+2+4+7+14=28Now knowing what a perfect number is, let's check 21Factors of 21 (excluding itself): 1,3 and 71+3+7=1111 is not equal to 21So 21 is not a perfect number
Is the number 21 abundant or deficient or perfect?
It is deficient: It's only proper divisors are 1, 3, and 7, which sums to 11, which is less than 21.
What is a mirror perfect number?
A perfect number is equal to the sum of its proper positive divisors.A mirror perfect number is equal to the sum of its proper positive divisors when they are read backwards.From a paper by Joseph L. Pe which is available on the 'net:10311 = 1 + 3 + 7 + 21 + 491 + 1473 + 34377343 + 3741 + 194 + 12 + 7 + 3 + 1 = 1130110311 is perfect and mirror perfect.
What is the sum of the first perfect number and the second perfect number?
The sum of the 1st perfect number and 2nd perfect number is. . . 34!
What is it called when a number has a whole number square root?
Then the number is called a "perfect square".Then the number is called a "perfect square".Then the number is called a "perfect square".Then the number is called a "perfect square".
What two square numbers total 21?
There is no pair of perfect squares that sums to 21. And the question is pointless if it is not about perfect squares because in that case there are infinitely many answers.There is no pair of perfect squares that sums to 21. And the question is pointless if it is not about perfect squares because in that case there are infinitely many answers.There is no pair of perfect squares that sums to 21. And the question is pointless if it is not about perfect squares because in that case there are infinitely many answers.There is no pair of perfect squares that sums to 21. And the question is pointless if it is not about perfect squares because in that case there are infinitely many answers.
Can a perfect number be odd?
If by 'perfect number' you mean 'perfect SQUARE', then yes. 49 is an odd number and a perfect square.
What is the third perfect number?
496 is the third perfect number and 8128 is the fourth perfect number.
What number is both a square number and a cube number between 1 and 25?
There is not a number that is a perfect square and perfect cube between 1 and 25.There is not a number that is a perfect square and perfect cube between 1 and 25.There is not a number that is a perfect square and perfect cube between 1 and 25.There is not a number that is a perfect square and perfect cube between 1 and 25.
