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Special exponent k=1k=1k=1: 1098 p<m21098\,p < m^{2}1098p<m2

Proved
OddPerfectNumber.k_one_special_prime_lt_sq

by Gabewhigham · Sep 11, 2026 · Mathlib 0df444a (Lean v4.33.1)

number-theory

Let N=p m2N = p\,m^{2}N=pm2 be an odd perfect number in Euler form with special exponent k=1k = 1k=1 (the configuration predicted by the Descartes–Frenicle–Sorli conjecture): ppp is prime, mmm is odd, p∤mp \nmid mp∤m, and the Dris relations

2m2=σ(p) s,σ(m2)=p s2m^{2} = \sigma(p)\,s, \qquad \sigma(m^{2}) = p\,s2m2=σ(p)s,σ(m2)=ps

hold, with s=σ(m2)/ps = \sigma(m^{2})/ps=σ(m2)/p the Dris index. Then the special prime is small compared with the square part:

1098 p < m2.1098\,p \ <\ m^{2}.1098p < m2.

Trivially σ(p)=p+1\sigma(p) = p+1σ(p)=p+1 divides 2m22m^{2}2m2, which alone gives only p<2m2p < 2m^{2}p<2m2. The point of the statement is the explicit constant: it comes from a lower bound s≥133=2197s \ge 13^{3} = 2197s≥133=2197 for the Dris index at k=1k = 1k=1, since 2m2=(p+1)s2m^{2} = (p+1)s2m2=(p+1)s. That lower bound in turn is a counting statement: at k=1k = 1k=1 the divisor sum σ(m2)=p s\sigma(m^{2}) = p\,sσ(m2)=ps has ppp-adic valuation 111, so at most one of the local divisor sums σ(q2vq(m))\sigma(q^{2v_q(m)})σ(q2vq​(m)), q∣mq \mid mq∣m, is divisible by ppp, and each of the others is a factor of sss of size at least 1+q+q2≥131 + q + q^{2} \ge 131+q+q2≥13. Sylvester's bound ω(N)≥5\omega(N) \ge 5ω(N)≥5 leaves at least three such factors.

The result is unconditional given the two Dris relations: no congruence conditions on ppp, mmm or sss are assumed.

Preamble
import Mathlib
Formal statement
namespace OddPerfectNumber

theorem k_one_special_prime_lt_sq (p m s : Nat)
    (hp : p.Prime) (hm : Odd m) (hpm : ¬ p ∣ m)
    (h1 : 2 * m ^ 2 = (∑ d ∈ p.divisors, d) * s)
    (h2 : (∑ x ∈ (m ^ 2).divisors, x) = p * s) :
    1098 * p < m ^ 2 := by
  sorry

end OddPerfectNumber
Source
J. A. B. Dris, The abundancy index of divisors of odd perfect numbers, Journal of Integer Seq. 15 (2012), Article 12.4.4, Section 2 (Dris parametrisation); J. J. Sylvester (1888) for omega(N) >= 5.

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