13 27 41 57 61 73 84 95 11 15 33 49 51 63 87 99 Which of these numbers are prime? What numbers are c

Prime numbers: 11 13 41 67 73

Composite number: 27 57 73 84 95 15 33 49 51 63 87 99

There are 25 prime numbers within 100, and we often use these prime numbers, which can be memorized in the following two ways.

1. Regular memory method.

First of all, remember 2 and 3, and the product of 2 and 3 prime numbers is the prime number within, which is generally in the position before and after the multiple of 6. Such as ......Only the numbers in the positions before and after these multiples of 6 are not prime numbers, and these numbers are multiples of 5 or 7. From this we can see:

The two numbers in the front and back positions of multiples of 6 within 100 must be prime numbers as long as they are not multiples of 5 or 7. Based on this feature, prime numbers up to 100 can be memorized.

2. Categorical mnemonics.

We can divide prime numbers within 100 into five categories of memory.

Category 1: Prime numbers within 20, a total of 8.

The second category: the single digit is 3 or 9, and the ten digits are 3 prime numbers, a total of 6.

The third category: the single digit is 1 or 7, and the ten-digit number is a prime number with a difference of 3, a total of 4.

Category 4: The single digit is or 7, and the ten digits are 3 prime numbers, a total of 5.

Category 5: There are 2 other holdings that are 79 and 97.

An easy way to test business.

Test quotient is the key to calculating the divisor is the three-digit division, when the divisor is close to the whole hundred, you can use the "rounding method" to test the quotient, but when the divisor is not close to the whole hundred, the test quotient is more difficult, and sometimes it is necessary to adjust the quotient many times. In order to help students solve this difficulty, the following is a simple way to test the business.

When dividing by tens of digits is 4, rounding off the mantissa is considered as an integer hundred. Use the whole hundred as the divisor to subtract 1 to test the quotient.

Naming such as 1944 243, except for the tens of digits is 4, 243 is regarded as 200, 1944 200 quotient 9, and it is appropriate to use 8 (9 1) to test quotient.

When dividing by tens of digits is , round off the mantissa to the hundredth digit by 1, regard the divisor as an integer hundred, and use the integer hundred as the divisor to add 1 to the quotient obtained by adding 1 to test the quotient.

For example: 1524 254 is divided by 5 in tens of places, 254 is regarded as 300, 1524 300 quotient 5, and it is appropriate to use 6 (5 1) to test quotient.

Using the above test quotient method, some can directly obtain the accurate quotient, and some only need to adjust the quotient once. Students don't try to try it when calculating division.

Prime numbers: 13 41 61 73 11

Everything else is a composite number.

A prime number, a number that has no divisor other than 1 and itself.

To put it simply, there are two ways to do this.

1. When using trial division to determine whether a natural number a is a prime number, use each prime number to remove a in order from small to large, if a prime number is exactly divisible, this a can be concluded that it is not a prime number; If it is not divisible, when the incomplete quotient is less than this prime number, there is no need to continue the trial division, and it can be concluded that a must be a prime number method.

2. As long as x is found to be an odd number and an even number in the form of the square difference (which is certain), then a2-b2 = (a+b) (a-b) are the two factors. For example, 26341, first find an even square number larger than 26341, 26896, and the difference between it is 555, which is definitely not a square number, and then the next square number (in fact, considering (x+1) 2=x2+2x+1, so just add the original number to 2x+1, and don't need to calculate the square of x+1), 27556, the difference is 1215, and it is not, and then the difference between 28224 single digits and 1 is 3, directly excluded, The next 2559 is not either (one look knows that it is equal to 50 2+59). Then the next difference is 3 and it is directly discharged, and then the next one, and then the next ......It is very quick to find the pattern, and finally 221 2 = 48841, 48841-26341 = 22500, obviously 22500 = 150 2, it is decomposed 26341 = 71 371

Prime numbers: 13, 41, 61, 73, 11, and the others are composites.

Composite number: 24 = 2 2 2 3

The prime number 1 is neither prime nor composite.

is a prime number and is a composite number.

Prime numbers are natural numbers that are greater than 1 and have no other factors other than 1 and themselves conform to that property, so they are prime numbers.

A composite number is a number of natural numbers that can be divisible by other numbers (except 0) in addition to 1 and itself. In addition to being divisible by 1 and itself, they are also divisible by 3, so they are composite numbers.

Note: 1 is neither a prime nor a composite number. The smallest composite number is 4.

Prime number. Composite numbers, and 1 are neither prime nor composite numbers.

1. All even numbers greater than 2 are composite. 2. Among all odd numbers greater than 5, the single digit of 5 is a composite number. 3. Except for 0, all natural numbers with a single digit of 0 are composite numbers.

4. All natural numbers with single digits of 4, 6, and 8 are composite numbers. 5. The minimum (even) composite number is 4.

There are 25 prime numbers within 100.

Prime number: In a natural number greater than 1, the number that cannot be divided by other natural numbers other than 1 and itself is a prime number.

So, there is .

Composite number, in the natural number of Chang width greater than 1, in addition to 1 and itself, the number that can be divisible by other natural numbers, is a composite number.

So, there is .

Odd numbers, in integers, the number that cannot be quickly divided by 2 is called an odd number.

So, there is .

Even numbers, in integers, numbers that are divisible by 2 are called even numbers.

So, there is .

Prime numbers, composite numbers, which macro is such as

Odd number: 99, Li hail book even number

In , the prime number has , and the composite number has =11 7.

17 and 91 and 81 and 54 and 23 and 77. Prime numbers are composed of 23 and 17, and the other 91, 81, 54, and 77 are all composite numbers.

Summary. 2. Composite number: It is a number in the natural number that can be divisible by other numbers (except 0) in addition to 1 and itself.

is a prime number, there is a composite number.

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Hello dear, the above prime numbers are: 3, 23, 97

If you add the composite number, there is no number that meets the standard.

The following is the definition of prime numbers

Prime numbers are also known as prime numbers. A natural number greater than 1 that is not divisible by other natural numbers except 1 and itself is called a prime number. The smallest prime number is 2, which is also the only even prime number.

The top prime numbers are: 2, 3, 5, 7, 11, etc. A number that is greater than 1 but is not a prime number is called a composite number.

1. Prime number: It is a natural number greater than 1, and there is no other factor except 1 and itself.

2. Composite number: It is a number in the natural number that can be divisible by other numbers (except 0) in addition to 1 and itself.

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There is only one number, 1, which is neither prime nor composite.

Because a prime number is a factor other than 1 and itself, a composite number is a factor other than 1 and itself.

So only 1 is not.

It can be combined like this:

1, 27, and 87, prime numbers have );

The composite number has );

There is (1) that is neither prime nor composite.

FYI.