209 research outputs found
Some vanishing sums involving binomial coefficients in the denominator
Identities involving binomial coeffcients usually arise in situations where counting is carried out in two different ways. For instance, some identities obtained by
William Horrace [1] using probability theory turn out to be special cases of the Chu-Vandermonde identities. Here, we obtain some generalizations of the identities observed by Horrace and give different types of proofs; these, in turn, give rise to some other new identities. In particular, we evaluate sums of the form Pm j=0 (1) j j d (mj) (n+jj )
and deduce that they vanish when d is even and m = n > d=2.
It is well-known [2] that sums involving binomial coeffcients can usually be expressed in terms of the hypergeometric functions but it is more interesting if such a function can be evaluated explicitly at a given argument. Identities such as the ones we prove could perhaps be of some interest due to the explicit evaluation possible.
The papers [3], [4] are among many which deal with identities for sums where the binomial coeffcients occur in the denominator and we use similar methods here
Tiresome paths, water gates and Euler’s formula
A hallmark of
mathematics is its
power to look at
seemingly different
problems with the
same eyes and find a
common idea which
resolves both. It is
not surprising that
the two problems
we discuss here,
about routes to be
taken with various
constraints and
about watering
fields, can both be
treated using ideas
from graph theor
Some Observations on Khovanskii\u27s Matrix Methods for extracting Roots of Polynomials
In this article we apply a formula for the n-th power of a 3×3 matrix (found previously by the authors) to investigate a procedure of Khovanskii’s for finding the cube root of a positive integer. We show, for each positive integer α, how to construct certain families of integer sequences such that a certain rational expression, involving the ratio of successive terms in each family, tends to α 1/3 . We also show how to choose the optimal value of a free parameter to get maximum speed of convergence. We apply a similar method, also due to Khovanskii, to a more general class of cubic equations, and, for each such cubic, obtain a sequence of rationals that converge to the real root of the cubic. We prove that Khovanskii’s method for finding the m-th (m ≥ 4) root of a positive integer works, provided a free parameter is chosen to satisfy a very simple condition. Finally, we briefly consider another procedure of Khovanskii’s, which also involves m×m matrices, for approximating the root of an arbitrary polynomial of degree m
Powers of a matrix and combinatorial identities
In this article we obtain a general polynomial identity in k variables, where k ≥ 2 is an arbitrary positive integer. We use this identity to give a closed-form expression for the entries of the powers of a k × k matrix. Finally, we use these results to derive various combinatorial identities
Binary Cubic Forms and Rational Cube Sum Problem
The classical Diophantine problem of determining which integers can be
written as a sum of two rational cubes has a long history; from the earlier
works of Sylvester, Satg{\'e}, Selmer etc. and up to the recent work of
Alp{\"o}ge-Bhargava-Shnidman. In this note, we use integral binary cubic forms
to study the rational cube sum problem. We prove (unconditionally) that for any
positive integer , infinitely many primes in each of the residue classes as well as , are sums of two rational cubes. Among
other results, we prove that every non-zero residue class , for
any prime , contains infinitely many primes which are sums of two rational
cubes. Further, for an arbitrary integer , we show there are infinitely many
primes in each of the residue classes and , such
that is a sum of two rational cubes
On a Conjecture of Chowlaet al.
AbstractWe prove some congruences for the numbers[formula]. In particular, we show that the numbers are congruent to 5 modulop3for any primep⩾5, thereby proving a conjecture of Chowlaet al.(J. Number Theory12(1980), 188–190)
Set theory revisited as easy as pie the principle of inclusion and exclusion – part 1
Recall the old story of two frogs from Osaka and Kyoto which meet during
their travels. They want to share a pie. An opportunistic cat offers to help and
divides the pie into two pieces. On finding one piece to be larger, she breaks
off a bit from the larger one and gobbles it up. Now, she finds that the other
piece is slightly larger; so, she proceeds to break off a bit from that piece and
gobbles that up, only to find that the first piece is now bigger. And so on; you
can guess the rest. The frogs are left flat
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