On odd perfect numbers with exactly one even exponent greater than 2
We show that if all the even exponents of an odd perfect number N are equal to 2 except for one, then $3^{23,000,000,000}$ divides N .
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arXiv subjects
Joshua Zelinsky
Publications and source records attributed to Joshua Zelinsky.
Complete characterization of $2$-near perfect numbers with exactly 2 prime factors
Let $\sigma(n)$ be the sum of the positive divisors of $n$. A positive integer $n$ is said to be $2$-near perfect when $\sigma(n)=2n+d_1+d_2$, where $d_1$ and $d_2$ are distinct positive divisors of $n$. We show that there are no odd $2$-near perfect numbers with exactly two prime factors, and that all even $2$-near perfect numbers (i.e. those of the form $2^kp^m$, where $p$ is an odd prime) belong to a specific family, provided that $m$ is at least 3. In combination with prior work, these results produce a complete characterization of $2$-near perfect numbers with exactly 2 prime factors.
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On near superperfect numbers, the Goormaghtigh conjecture, and Mertens' theorem
Let $\sigma(n)$ be the sum of the divisors of $n$. Kalita and Saikia defined a number $n$ to be near superperfect if $2n+d=\sigma(\sigma(n))$ for some positive divisor $d$ of $n$. We extend some of their results about near superperfect numbers and connect these results to the Goormaghtigh conjecture and to certain products of primes similar to those which appear in Mertens' theorem. We also define type II near superperfect numbers, which are those $n$ which satisfy $2n+d=\sigma(\sigma(n))$ for some positive divisor $d$ of $\sigma(n)$, and prove analogous results about these numbers.
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Kullback-Leibler divergence and primitive non-deficient numbers
Let $H(n) = \prod_{p|n}\frac{p}{p-1}$ where $p$ ranges over the primes which divide $n$. It is well known that if $n$ is a primitive non-deficient number, then $H(n) > 2$. We examine inequalities of the form $H(n)> 2 + f(n)$ for various functions $f(n)$ where $n$ is assumed to be primitive non-deficient and connect these inequalities to applying the Kullback-Leibler divergence to different probability distributions on the set of divisors of $n$.
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Dots and Boxes on Certain Families of Graphs
We investigate the Dots and Boxes game, also known as ``Strings and Coins,'' for certain specific families of graphs. These include complete graphs, wheel graphs, and friendship graphs.
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The sum of the reciprocals of the prime divisors of an odd perfect or odd primitive non-deficient number
Write $T(n)$ as the sum of the reciprocals of the primes which divide $n$. Write $H(n) = \prod_{p|n}p/(p-1)$ where the product is over the prime divisors of $n$. We prove new bounds for $T(n)$ and $H(n)$ in terms of the smallest prime factor of $n$, under the assumption that $n$ is an odd perfect number. Some of the results also apply under the weaker assumption that $n$ is odd and primitive non-deficient.
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Weighted Versions of the Arithmetic-Mean-Geometric Mean Inequality and Zaremba's Function
We use the weighted version of the arithmetic-mean-geometric-mean inequality to motivate new results about Zaremba's function, $z(n) = \sum_{d|n} \frac{\log d}{d}$. We investigate record-setting values for $z(n)$ and the related function $v(n) = \frac{z(n)}{\log \tau(n)}$ where $\tau(n)$ is the number of divisors of $n$. We show that $v(n)$ takes on a maximum value and we give a list of all record-setting values for$v(n)$. Closely connected inequalities motivate the study of numbers which are pseudoperfect in a strong sense.
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A Note on a Result of Makowski
In this note, we fix a gap in a proof of the first author that 28 is the only even perfect number which is the sum of two perfect cubes. We also discuss the situation for higher powers.
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On 2-Near Perfect Numbers
Let $\sigma(n)$ be the sum of the positive divisors of $n$. A number $n$ is said to be 2-near perfect if $\sigma(n) = 2n +d_1 +d_2 $, where $d_1$ and $d_2$ are distinct positive divisors of $n$. We give a complete description of those $n$ which are 2-near perfect and of the form $n=2^k p^i$ where $p$ is prime and $i \in \{1,2\}$. We also prove related results under the additional restriction where $d_1d_2=n$.
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On the small prime factors of a non-deficient number
Let $σ(n)$ to be the sum of the positive divisors of $n$. A number is non-deficient if $σ(n) \geq 2n$. We establish new lower bounds for the number of distinct prime factors of an odd non-deficient number in terms of its second smallest, third smallest and fourth smallest prime factors. We also obtain tighter bounds for odd perfect numbers. We also discuss the behavior of $σ(n!+1)$, $σ(2^n+1)$, and related sequences.
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Upper Bounds on Integer Complexity
Define $||n||$ to be the \emph{complexity} of $n$, which is the smallest number of $1$s needed to write $n$ using an arbitrary combination of addition and multiplication. John Selfridge showed that $||n|| \geq 3\log_3 n$ for all $n$. Richard Guy noted the trivial upper bound that $||n|| \leq 3\log_2 n$ for all $n>1$ by writing $n$ in base 2. An upper bound for almost all $n$ was provided by Juan Arias de Reyna and Jan Van de Lune. This paper provides the first non-trivial upper bound for all $n$. In particular, for all $n>1$ we have $||n|| \leq A \log n$ where $A = \frac{41}{\log 55296}$.
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Total Difference Labeling of Regular Infinite Graphs
Given a graph $G$, a \textit{$k$-total difference labeling} of the graph is a total labeling $f$ from the set of edges and vertices to the set $\{1, 2, \cdots k\}$ satisfying that for any edge $\{u,v\}$, $f(\{u,v\})=|f(u)-f(v)|$. If $G$ is a graph, then $\chi_{td}(G)$ is the minimum $k$ such that there is a $k$-total difference labeling of $G$ in which no two adjacent labels are identical. We extend prior work on total difference labeling by improving the upper bound on $\chi_{td}(K_n)$ and also by proving results concerning infinite regular graphs.
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On the third largest prime divisor of an odd perfect number
Let $N$ be an odd perfect number and let $a$ be its third largest prime divisor, $b$ be the second largest prime divisor, and $c$ be its largest prime divisor. We discuss steps towards obtaining a non-trivial upper bound on $a$, as well as the closely related problem of improving bounds $bc$, and $abc$. In particular, we prove two results. First we prove a new general bound on any prime divisor of an odd perfect number and obtain as a corollary of that bound that $$a < 2N^{\frac{1}{6}}.$$ Second, we show that $$abc < (2N)^{\frac{3}{5}}.$$ We also show how in certain circumstances these bounds and related inequalities can be tightened. Define a $σ_{m,n}$ pair to be a pair primes $p$ and $q$ where $q|σ(p^m)$, and $p|σ(q^n)$. Many of our results revolve around understanding $σ_{2,2}$ pairs. We also prove results concerning $σ_{m,n}$ pairs for other values of $m$ and $n$.
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Must a primitive non-deficient number have a component not much larger than its radical?
Let $n$ be a primitive non-deficient number where $n=p_1^{a_1}p_2^{a_2} \cdots p_k^{a_k}$ where $p_1, p_2, \cdots, p_k$ are distinct primes. We prove that there exists an $i$ such that $$p_i^{a_i+1} < 2k(p_1p_2p_3\cdots p_k).$$ We conjecture that in fact one can always find an $i$ such that $p_i^{a_i+1} < 2p_1p_2p_3\cdots p_k$.
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On the number of total prime factors of an odd perfect number
Let $N$ be an odd perfect number. Let $ω(N)$ be the number of distinct prime factors of $N$ and let $Ω(N)$ be the total number of prime factors of $N$. We prove that if $(3,N)=1$, then $ \frac{302}{113}ω- \frac{286}{113} \leq Ω. $ If $3|N$, then $\frac{66}{25}ω-5\leqΩ.$ This is an improvement on similar prior results by the author which was an improvement of a result of Ochem and Rao. We also establish new lower bounds on $ω(N)$ in terms of the smallest prime factor of $N$ and establish new lower bounds on $N$ in terms of its smallest prime factor.
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Upper bounds on the second largest prime factor of an odd perfect number
Acquaah and Konyagin showed that if $N$ is an odd perfect number where $N= p_1^{a_1}p_2^{a_2} \cdots p_k^{a_k}$ where $p_1 < p_2 \cdots < p_k$ then one must have $p_k < 3^{1/3}N^{1/3}$. Using methods similar to theirs, we show that $p_{k-1}< (2N)^{1/5}$ and that $p_{k-1}p_k < 6^{1/4}N^{1/2}.$ We also show that if $p_k$ and $p_{k-1}$ are close to each other than these bounds can be further strengthened.
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An improvement of an inequality of Ochem and Rao concerning odd perfect numbers
Let $Ω(n)$ denote the total number of prime divisors of $n$ (counting multiplicity) and let $ω(n)$ denote the number of distinct prime divisors of $n$. Various inequalities have been proved relating $ω(N)$ and $Ω(N)$ when $N$ is an odd perfect number. We improve on these inequalities. In particular, we show that if $3 \not| N$, then $Ω\geq \frac{8}{3}ω(N)-\frac{7}{3}$ and if $3 |N$ then $Ω(N) \geq \frac{21}{8}ω(N)-\frac{39}{8}.$
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Upper bounds for the number of primitive ray class characters with conductor below a given bound
We present upper bounds on certain sums which are related to Artin's primitive root conjecture and are also used in counting ray class characters.
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