In the 72 numbers of 1-72, how many are coprime numbers with 72

In the 72 numbers of 1-72, how many are coprime numbers with 72

1 5 7 11 13 17 19 23 25 29 31 35 37 41 43 47 49 53 55 59 61 65 67 71
Qiudi 70's answer is wrong, he missed 35, 49 and 59, 51 and 57 more

Finding the number of Coprime numbers with a prime number
N is a prime number and K is the number of Coprime numbers
Prove k = n-1
How can I prove it?
Forget to say that K is the number of numbers less than N and prime to each other in n

Odd number: not divisible by two (such as "3")
Even number: divisible by two (e.g. "2")
Prime number: except one and itself, no other number can divide it (such as "5")
The explanation that 1 is neither prime nor composite
Prime number: a number is called a prime number if it has only 1 and its own two factors and no other factors
Composite number: in addition to 1 and itself, there are other factors that are composite numbers
1 has only one factor. Therefore, 1 is neither prime nor composite
Natural number is divided into 1, prime number and composite number
Here are all prime numbers up to 1000
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 101 103 107 109 113 127 131 137 139 149 151 157 163 167 173 179 181 191 193 197 199 211 223 227 229 233 239 241 251 257 263 269 271 277 281 283 293 307 311 313 317 331 337 347 349 353 359 367 373 379 383 389 397 401 409 419 421 431 433 439 443 449 457 461 463 467 479 487 491 499 503 509 521 523 541 547 557 563 569 571 577 587 593 599 601 607 613 617 619 631 641 643 647 653 659 661 673 677 683 691 701 709 719 727 733 739 743 751 757 761 769 773 787 797 809 811 821 823 827 829 839 853 857 859 863 877 881 883 887 907 911 919 929 937 941 947 953 967 971 977 983 991 997
Coprime number
The definition of Coprime number in primary school mathematics textbook is as follows: "two numbers with only one common divisor are called coprime numbers."
The "two numbers" here refer to natural numbers
Common divisor
Like 4 and 6
The divisor of 4 is 1,2,4
The divisor of 6 is 1,2,3,6
So 1 and 2 are their common divisors. The greatest positive common divisor is 2 and the least common divisor is 1
1 is a multiple of any number, but it is coprime with any number. Because the factor of 1 is only 1, and the principle of Coprime number is: as long as the common factor of two numbers is only 1, it is said that two numbers are coprime. 1 has only one factor (so 1 is neither prime nor composite), and there is no other common factor between 1 and other numbers, so 1 and any number are coprime