Proof of Theorem 2. We employ a modification of Wirsing’s method from [9]. Sup- pose that N ≤ x is odd and perfect and ω(N ) ≤ k. (If there are no such N , then
the theorem holds trivially, since the quantity (log x)k is nonnegative.) Let p0 be the least prime divisor of N , and let e0 ≥ 1 be such that pe0 I N . Put B := pe0
0 0
and write N = AB. Then A and B are relatively prime, and so (since σ is a
multiplicative function)