9 (9), 15 ( 15), 2 1 (2 1), 25 (25), 27 (27), 33 (33), 35 (35), 39 (39), 45 (45), 49 (49), 50.77 (77), 8 1 (8 1), 85 (85), 87 (87), 9 1 (9 1), 93 (93), 95 (95), 99 (99).

Among the integers, the number divisible by 2 is even, the number divisible by 2 is odd, and the odd number is 1, 3, 5, 7, 9. Even numbers can be represented by 2k, and odd numbers can be represented by 2k+ 1, where k is an integer.

Composite number refers to the number divisible by other numbers (except 0) except 1 and itself in natural numbers. In contrast, it is a prime number, and 1 is neither a prime number nor a composite number. The smallest composite number is 4. Among them, the perfect number and the number of blind dates are based on this.

Extended data:

Regarding odd and even numbers, there are the following properties:

(1) Two consecutive integers must have an odd number and an even number;

(2) Odd number+odd number = even number; Even+odd = odd; Even number+even number+...+even number = even number;

(3) Odd-odd = even; Parity = odd number; Odd-even = odd;

(4) If A and B are integers, the parity of a+b and a-b is the same, that is, a+b and a-b are both odd or even;

(5) The product of n odd numbers is odd, and the product of n even numbers is even; If one of the formulas is even, the product is even;

(6) Odd numbers are 1, 3, 5, 7 and 9; Even numbers are 0, 2, 4, 6, 8;

(7) Divide the square of odd numbers by 2, 4 and 8, and the remainder is1;

(8) The square difference of any two odd numbers is a multiple of 2, 4 and 8;

(9) The remainder of an odd number divided by 2 is 1.

The prime numbers within 100 are 2,3,5,7, 1 1 3, 17,19,23,29,31.

Whether the number is a prime number or a composite number, it means that there are other prime numbers besides the assumed finite number of prime numbers. So the original assumption doesn't hold water. In other words, there are infinitely many prime numbers.

Baidu encyclopedia-odd number

Baidu encyclopedia-composite number