```
/*
author sandyboypraper
Here is the EulerTotientFunction.
it is also represented by phi
so EulersTotientFunction(n) (or phi(n)) is the count of numbers in {1,2,3,....,n} that are relatively
prime to n, i.e., the numbers whose GCD (Greatest Common Divisor) with n is 1.
*/
const gcdOfTwoNumbers = (x, y) => {
// x is smaller than y
// let gcd of x and y is gcdXY
// so it divides x and y completely
// so gcdXY should also divide y%x (y = gcdXY*a and x = gcdXY*b and y%x = y - x*k so y%x = gcdXY(a - b*k))
// and gcd(x,y) is equal to gcd(y%x , x)
return x === 0 ? y : gcdOfTwoNumbers(y % x, x)
}
const eulersTotientFunction = (n) => {
let countOfRelativelyPrimeNumbers = 1
for (let iterator = 2; iterator <= n; iterator++) {
if (gcdOfTwoNumbers(iterator, n) === 1) countOfRelativelyPrimeNumbers++
}
return countOfRelativelyPrimeNumbers
}
export { eulersTotientFunction }
```

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