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It is deficient: It's only proper divisors are 1, 3, and 7, which sums to 11, which is less than 21.

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Q: Is the number 21 abundant or deficient or perfect?

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Non-perfect square numbers are numbers that are not formed from the square of a number. 12, 13, 14, 21, 99, etc, are all non-perfect square numbers because when you square root them you do not get a whole number, which means they are not formed by any whole number, x, being squared (x^2).

21 over 10 as a mixed number is 21/10

The divisors of 21 are: 1, 3, 7, 21.

the answer will be 21

When figuring out what number goes both into 21 and 28, you should look at the factor paris. 21: 1 x 21, 3 x 7 28: 1, 28, 2 x 14, 4 x 7 7 goes into both 21 and 28.

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Deficient number From Wikipedia, the free encyclopediaIn mathematics, a deficient number or defective number is a number n for which Ïƒ(n) < 2n. Here Ïƒ(n) is the sum-of-divisors function: the sum of all positive divisors of n, including nitself. An equivalent definition is that the sum of all proper divisors of the number (divisors other than the number itself) is less than the number. The value 2n âˆ’ Ïƒ(n) is called the deficiency of n.The first few deficient numbers are: 1, 2, 3, 4, 5, 7, 8, 9, 10, 11, 13, 14, 15, 16, 17, 19, 21, 22, 23, 25, 26, 27, â€¦ (sequence A005100 in OEIS)As an example, consider the number 21. Its divisors are 1, 3, 7 and 21, and their sum is 32. Because 32 is less than 2 Ã— 21, the number 21 is deficient. Its deficiency is 2 Ã— 21 âˆ’ 32 = 10.An infinite number of both even and odd deficient numbers exist. For example, all odd numbers with one or two distinct prime factors, and all proper divisors of deficient or perfect numbers are deficient.Closely related to deficient numbers are perfect numbers with Ïƒ(n) = 2n, and abundant numbers with Ïƒ(n) > 2n. The natural numbers were first classified as either deficient, perfect or abundant byNicomachus in his Introductio Arithmetica (circa 100).

A deficient number is a number for which the sum of its positive integer factors (other than itself) is less than itself. The sum of the factors of 18 is 1 + 2 + 3 + 6 + 9 = 21. Since 21 is greater than 18, 18 is an abundant number.

2: 1, 2 (3) deficient 3: 1, 3 (4) deficient 4: 1, 2, 4 (7) deficient 5: 1, 5 (6) deficient 6: 1, 2, 3, 6 (12) perfect 7: 1, 7 (8) deficient 8: 1, 2, 4, 8 (15) deficient 9: 1, 3, 9 (13) deficient 10: 1, 2, 5, 10 (18) deficient 11: 1, 11 (12) deficient 12: 1, 2, 3, 4, 6, 12 (28) abundant 13: 1, 13 (14) deficient 14: 1, 2, 7, 14 (24) deficient 15: 1, 3, 5, 15 (24) deficient 16: 1, 2, 4, 8, 16 (31) deficient 17: 1, 17 (18) deficient 18: 1, 2, 3, 6, 9, 18 (39) abundant 19: 1, 19 (20) deficient 20: 1, 2, 4, 5, 10, 20 (42) abundant 21: 1, 3, 7, 21 (32) deficient 22: 1, 2, 11, 22 (26) deficient 23: 1, 23 (24) deficient 24: 1, 2, 3, 4, 6, 8, 12, 24 (60) abundant 25: 1, 5, 25 (31) deficient 26: 1, 2, 13, 26 (42) deficient 27: 1, 3, 9, 27 (40) deficient 28: 1, 2, 4, 7, 14, 28 (56) perfect 29: 1, 29 (30) deficient 30: 1, 2, 3, 5, 6, 10, 15, 30 (72) abundant

It is a number for which the sum of the proper divisors is less the the number. Example: 21 has divisors 1, 3, and 7. The sum is 11 which is less than 21. Note: All prime numbers are deficient and as there are an infinite number of them, there are an infinite set of deficient numbers too.

An Abundant Number is one that the factors (other than itself) add up to more than the number. 18 factors into [2 3 3] so the factor list is {1 2 3 6 9 18} and the sum of the rest is 21. Since 21 is greater than 18, it is an abundant number.Yes 18 is an abundant number because if you add all of it's factors (1,2,3,6,9,) together the sum is 21.Definition of Abundant- a number that is less the sum of it's factors or integers

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.

21

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.

sorry mans it's not but on the bright side 28 is :)

42.0 Properties: -Composite -Square-Free -Semi-Perfect -Practical -Abundant -Highly Abundant Factors: 1, 2, 3, 6, 7, 14, 21, 42. Prime Factorization: 2 x 3 x 7 Number of factors: 8 Sum of factors: 96.0 Sigma Ratio: 2.2857142857142856

It is oxygen about 21% the most abundant is nitrogen about 78%.

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

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