1. Define the functions and the problem statement:
- Let φ(m) be the Euler's totient function, which counts the number of positive integers up to m that are relatively prime to m.
- Let σ(m) be the sum of the positive divisors of m.
- We need to find the sum of all even positive integers n such that
φ(n)n5σ(n)−2
is an integer.
2. **Express n in terms of its prime factors:**
- Let n=2ap1a1p2a2⋯pkak where pi are odd primes.
- The Euler's totient function for n is:
φ(n)=φ(2a)φ(p1a1)φ(p2a2)⋯φ(pkak)
Since φ(2a)=2a−2a−1=2a−1 for a≥1, and φ(piai)=piai−piai−1.
3. Analyze the divisibility condition:
- We need φ(n)n5σ(n)−2 to be an integer.
- Consider the 2-adic valuation v2 of φ(n):
v2(φ(n))=(a−1)+v2(φ(p1a1))+v2(φ(p2a2))+⋯+v2(φ(pkak))
Since pi are odd primes, v2(φ(piai))=0. Thus,
v2(φ(n))=a−1
4. **Evaluate v2(n5σ(n)−2):**
- For n=2ap1a1p2a2⋯pkak, n5σ(n) is even, so n5σ(n)−2 is odd.
- Therefore, v2(n5σ(n)−2)=1.
5. Set up the inequality:
- We need v2(n5σ(n)−2)≥v2(φ(n)):
1≥a−1
This implies:
a≤2
6. **Consider possible values of a and k:**
- If a=1, then n=2p where p is an odd prime.
- If a=2, then n=4.
7. Evaluate specific cases:
- For n=2p:
φ(2p)=p−1,σ(2p)=(1+2)(1+p)=3(p+1)
We need:
p−1(2p)5⋅3(p+1)−2 to be an integer
Simplifying:
p−196p6+96p5−2
This implies p−1 must divide 190. Possible values of p−1 are 2, 10, 190, giving p=3,11,191.
- For n=4:
φ(4)=2,σ(4)=1+2+4=7
We need:
245⋅7−2=27166=3583 which is an integer
8. **Sum the valid n values:**
- Valid n values are 2,4,6,22,382.
- Sum: 2+4+6+22+382=416.