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arXiv 1002.3254math.NT
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基于Φ函数和互素子集的组合恒等式

Combinatorial Identities Via Phi Functions and Relatively Prime Subsets

Mohamed El Bachraoui

摘要:

设$n$是正整数,$A$是正整数的非空有限集.我们说,如果$\gcd(A) =1$是相对素的,如果$\gcd(A,n)=1$是相对素的,则$A$与$n$是互素的。在这项工作中,我们计数的非空子集的$A$是互素和非空子集的$A$是互素$n$的数量。对于具有固定基数的子集的个数,也得到了相关的公式。这扩展了以前的工作的情况下,$A$是一个区间或一组等差数列。应用包括:a)得到了$A$中与$n$互素的元素个数的精确公式;注意,如果$A=[1,n]$,则该个数为$ϕ(n)$。b)给出了正整数的非空有限集的元素都是两两互质的代数特征,并由此给出了$A$的元素都是两两互质的非空子集的个数公式. c)给出了包含Mertens函数的组合公式。

英文摘要:

Let $n$ be a positive integer and let $A$ be nonempty finite set of positive integers. We say that $A$ is relatively prime if $\gcd(A) =1$ and that $A$ is relatively prime to $n$ if $\gcd(A,n)=1$. In this work we count the number of nonempty subsets of $A$ which are relatively prime and the number of nonempty subsets of $A$ which are relatively prime to $n$. Related formulas are also obtained for the number of such subsets having some fixed cardinality. This extends previous work for the cases where $A$ is an interval or a set in arithmetic progression. Applications include: a) An exact formula is obtained for the number of elements of $A$ which are co-prime to $n$; note that this number is $ϕ(n)$ if $A=[1,n]$. b) Algebraic characterizations are found for a nonempty finite set of positive integers to have elements which are all pairwise co-prime and consequently a formula is given for the number of nonempty subsets of $A$ whose elements are pairwise co-prime. c) We provide combinatorial formulas involving Mertens function.

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