P^2+Σ2P

You need to go back the start point in Eulerian trail. You can go through the path once. This is closed . Each edge has even links.

A perfect number is a number that is half the sum of all of its positive divisors, and it is including itself. σ(N)=2N 28 is the perfect number. 28=1 + 2 + 4 + 7 + 14 σ(28)=1 + 2 + 4 + 7 + 14 + 28 = 2*28 = 56 Euler proved that all even perfect numbers were in the Euclid–Euler theorem. The sum of divisors of a number must include the number itself, not just the proper divisors. σ(2^2(2^3-1))=σ(4)σ(7)=(1+2+4)(1+7)=7*8=56=σ(28) This is known as Mersenne primes. 2(2^2-1)=6 2^2(2^3-1)=28 2^4(2^5-1)=496 These are perfect numbers. 3,7,31 are primes, so you can find perfect numbers infinitely because of fractal . However, odd perfect numbers are unknown.