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Research notes on every problem, and a library of the papers behind them. Built from the open erdos repository.

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What prime-gap statistics would imply


Put dn=pn+1−pnd_n=p_{n+1}-p_n. These are author-recorded comparisons of the target statements. They do not establish the conjectured prime-gap laws.

Support is stronger than existence of a distribution

Problem 234 asks for a continuous limiting distribution of dn/log⁡nd_n/\log n. If such a distribution FF gives positive mass to every open interval in (0,∞)(0,\infty) and to every interval (0,b)(0,b), then every c≥0c\ge0 is a limit point, as requested by Problem 5. For c>0c>0, take arbitrarily small intervals about cc with positive mass; convergence of their frequencies gives infinitely many indices in each interval. Choose an increasing sequence of those indices. For c=0c=0, use (0,1/j)(0,1/j) instead. Since log⁡pn/log⁡n→1\log p_n/\log n\to1, the normalizations have the same finite limit points.

Continuity alone does not supply full support. The conditional exponential distribution reported on Problem 234 has it, but its prime-tuple hypothesis remains unproved. The unconditional positive measure and bounded-gap properties of the set of limit points do not give full support either. For example, ⋃j≥0[j,j+1/2]\bigcup_{j\ge0}[j,j+1/2] is a proper closed subset of [0,∞)[0,\infty), has measure at least T/2T/2 in [0,T][0,T], and meets every interval of length one. This example tests only those two consequences, not all the stronger combinatorial assertions in Merikoski's paper. Its Theorem 1 and Corollaries 2--3 were inspected at statement depth. The next test for a proposed route is positive limiting mass in an arbitrary prescribed interval. Stop if the available conclusion only bounds total measure or gaps in the set of limit points.

Two half-density inequalities do not prove infinitely many equalities

For Problem 218, let ANA_N count n≤Nn\le N with dn+1≥dnd_{n+1}\ge d_n, let BNB_N count those with dn+1≤dnd_{n+1}\le d_n, and let ENE_N count equalities. Then AN+BN=N+ENA_N+B_N=N+E_N. Thus AN/N→1/2A_N/N\to1/2 and BN/N→1/2B_N/N\to1/2 together imply EN/N→0E_N/N\to0, not EN→∞E_N\to\infty. The numerical sequence alternating between 22 and 44 has both inequality densities 1/21/2 and no equality; this is a logical example, not a prime-gap construction. Marginal distributions of individual gaps likewise do not determine adjacent pairs. [[../library/primes/banks_2023_ratios_consecutive_prime_gaps/_index|Banks's ratio formula]] is presented as a conjecture motivated by a heuristic, not an unconditional adjacent-gap theorem. A route must supply both the needed joint distribution and a separate reason for infinitely many exact equalities.

A second moment still leaves a power-sized distinct run

Let M2(N)=∑n≤Ndn2M_2(N)=\sum_{n\le N}d_n^2. Cauchy--Schwarz and the prime number theorem give M2(N)≫N(log⁡N)2M_2(N)\gg N(\log N)^2, so Problem 233 asks for an upper bound of the correct order. The inspected Theorem 1 of Stadlmann is instead ∑pn≤Xdn2≪εX1.23+ε\sum_{p_n\le X}d_n^2\ll_\varepsilon X^{1.23+\varepsilon}. Changing from prime value XX to index NN does not remove its excess power.

Even the desired bound would only give a power estimate for the length HH of a run of pairwise distinct gaps starting at index n<xn<x, the quantity in Problem 852. Distinct positive integers have sum at least H(H+1)/2H(H+1)/2. The telescoping sum of these gaps is at most pn+H≪(x+H)log⁡(x+H)p_{n+H}\ll(x+H)\log(x+H). For large xx this first forces H<xH<x, and then H≪xlog⁡xH\ll\sqrt{x\log x}. The run therefore ends before 2x2x. Its squared gaps have sum at least ∑j=1Hj2≫H3\sum_{j=1}^Hj^2\gg H^3, while the hypothetical bound for Problem 233 gives M2(2x)≪x(log⁡x)2M_2(2x)\ll x(\log x)^2. Consequently

H≪(x(log⁡x)2)1/3.H\ll\bigl(x(\log x)^2\bigr)^{1/3}.

This is far above o(log⁡x)o(\log x). It is a limitation of this direct moment argument, not a proof that Problem 233 could never help by another method. A useful next test must exploit local repetition or dependence beyond a global second moment; stop the bare sum-of-squares route at the displayed bound.

First occurrences and Problem 853

For a positive even integer tt, let τ(t)=min⁡{n:dn=t}\tau(t)=\min\{n:d_n=t\}, with τ(t)=∞\tau(t)=\infty if no such index exists. For real y≥2y\ge2 put T(y)=max⁡2≤t≤y, 2∣tτ(t)T(y)=\max_{2\le t\le y,\ 2\mid t}\tau(t). In the notation of Problem 853, r(x)r(x) is the least missing positive even gap among indices n≤xn\le x. The positivity convention matters: including zero among candidate gap sizes would make r(x)r(x) identically zero. Exactly

r(x)>y⟺T(y)≤x.(1)r(x)>y\quad\Longleftrightarrow\quad T(y)\le x.\tag{1}

It follows that r(x)→∞r(x)\to\infty is equivalent to every positive even gap occurring at least once. Infinitely many occurrences of each gap would be stronger than needed. The stronger requested conclusion is equivalent to

T(y)<∞ for every y,log⁡T(y)=o(y).(2)T(y)<\infty\text{ for every }y,\qquad \log T(y)=o(y).\tag{2}

Indeed, if r(x)/log⁡x→∞r(x)/\log x\to\infty, take x=exp⁡(εy)x=\exp(\varepsilon y). Eventually r(x)>yr(x)>y, so T(y)≤exp⁡(εy)T(y)\le\exp(\varepsilon y) for every fixed ε>0\varepsilon>0. Conversely, fix K>0K>0 and use (2) with ε<1/K\varepsilon<1/K. For y=Klog⁡xy=K\log x and all sufficiently large xx, T(y)≤exp⁡(εy)<xT(y)\le\exp(\varepsilon y)<x, so (1) gives r(x)>Klog⁡xr(x)>K\log x. Integer rounding changes neither conclusion. This exact interface exposes the hard step: a subexponential upper bound for the worst first occurrence, uniform over all even t≤yt\le y. A fixed-pattern existence theorem with uncontrolled constants does not supply (2). Stop a proposed deduction if its threshold still depends ineffectively on each individual tt.

Adjacent near-record gaps and Problem 1137

For integer N≥2N\ge2, define

DN=max⁡1≤n≤Ndn,MN=max⁡2≤n≤Ndndn−1,BN=max⁡2≤n≤Nmin⁡(dn,dn−1).D_N=\max_{1\le n\le N}d_n,\quad M_N=\max_{2\le n\le N}d_nd_{n-1},\quad B_N=\max_{2\le n\le N}\min(d_n,d_{n-1}).

Both factors in every product are bounded by DND_N, hence

BN2≤MN≤DNBN.B_N^2\le M_N\le D_NB_N.

Thus Problem 1137 is equivalent to BN/DN→0B_N/D_N\to0. Equivalently, for every ε>0\varepsilon>0, all sufficiently large prefixes contain no adjacent pair both at least εDN\varepsilon D_N. The omitted initial undefined product and changing n<xn<x to an integer prefix have no asymptotic effect. This is a relative isolation assertion. A lower bound for one large gap, such as Theorem 1 of [[../library/primes/maynard_2016_large_gaps_between_primes/_index|Maynard's large-gap paper]], gives no such upper bound for adjacent products. A route must control the smaller member of every adjacent pair relative to the running maximum. Stop before inferring isolation from a single-gap construction, even if that construction substantially increases DND_N.