Harmonic progression (mathematics)

Last updated October 26, 2024

In mathematics, a harmonic progression (or harmonic sequence) is a progression formed by taking the reciprocals of an arithmetic progression, which is also known as an arithmetic sequence.

Examples

In the following $n$ is a natural number, in sequence: $\ n=1,\ 2,\ 3,\ 4,\ \ldots \$

$1,{\tfrac {\ 1\ }{2}},\ {\tfrac {\ 1\ }{3}},\ {\tfrac {\ 1\ }{4}},\ {\tfrac {\ 1\ }{5}},\ {\tfrac {\ 1\ }{6}},\ \ldots \ ,\ {\tfrac {\ 1\ }{n}},\ \ldots \$ is called the harmonic sequence
12, 6, 4, 3, $\ {\tfrac {12}{\ 5\ }},\ 2,\ \ldots \ ,\ {\tfrac {12}{\ n\ }},\ \ldots \$
30, −30, −10, −6, $\ -{\tfrac {30}{\ 7\ }},\ \ldots \ ,\ {\tfrac {30}{\ \left(3\ -\ 2n\right)\ }},\ \ldots \$
10, 30, −30, −10, −6, $\ \ldots \ {\tfrac {30}{\ \left(5\ -\ 2n\right)\ }},\ \ldots \$

Sums of harmonic progressions

Infinite harmonic progressions are not summable (sum to infinity).

It is not possible for a harmonic progression of distinct unit fractions (other than the trivial case where a = 1 and k = 0) to sum to an integer. The reason is that, necessarily, at least one denominator of the progression will be divisible by a prime number that does not divide any other denominator.^[1]

Use in geometry

If collinear points A, B, C, and D are such that D is the harmonic conjugate of C with respect to A and B, then the distances from any one of these points to the three remaining points form harmonic progression.^[2]^[3] Specifically, each of the sequences AC, AB, AD; BC, BA, BD; CA, CD, CB; and DA, DC, DB are harmonic progressions, where each of the distances is signed according to a fixed orientation of the line.

In a triangle, if the altitudes are in arithmetic progression, then the sides are in harmonic progression.

Leaning Tower of Lire

An excellent example of Harmonic Progression is the Leaning Tower of Lire. In it, uniform blocks are stacked on top of each other to achieve the maximum sideways or lateral distance covered. The blocks are stacked 1/2, 1/4, 1/6, 1/8, 1/10, … distance sideways below the original block. This ensures that the center of gravity is just at the center of the structure so that it does not collapse. A slight increase in weight on the structure causes it to become unstable and fall.

Related Research Articles

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In mathematics, the harmonic mean is a kind of average. It is one of the three Pythagorean means.

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In mathematics, a continued fraction is an expression obtained through an iterative process of representing a number as the sum of its integer part and the reciprocal of another number, then writing this other number as the sum of its integer part and another reciprocal, and so on. In a finite continued fraction, the iteration/recursion is stopped after finitely many steps by using an integer in lieu of another continued fraction. In contrast, an infinite continued fraction is an infinite expression. In either case, all integers in the sequence, other than the first, must be positive. The integers $are called the coefficients or terms of the continued fraction.$

In mathematics, Pascal's triangle is an infinite triangular array of the binomial coefficients which play a crucial role in probability theory, combinatorics, and algebra. In much of the Western world, it is named after the French mathematician Blaise Pascal, although other mathematicians studied it centuries before him in Persia, India, China, Germany, and Italy.

<span class="mw-page-title-main">Euler's totient function</span> Number of integers coprime to and less than n

In number theory, Euler's totient function counts the positive integers up to a given integer $n$ that are relatively prime to $n$ . It is written using the Greek letter phi as $or, and may also be called Euler's phi function . In other words, it is the number of integers k in the range 1 \leq k \leq n for which the greatest common divisor gcd(n, k) is equal to 1. The integers k of this form are sometimes referred to as totatives of n .$

In mathematics, the harmonic series is the infinite series formed by summing all positive unit fractions:

<span class="mw-page-title-main">Euler's constant</span> Constant value used in mathematics

Euler's constant is a mathematical constant, usually denoted by the lowercase Greek letter gamma, defined as the limiting difference between the harmonic series and the natural logarithm, denoted here by $log$ :

An arithmetic progression or arithmetic sequence is a sequence of numbers such that the difference from any succeeding term to its preceding term remains constant throughout the sequence. The constant difference is called common difference of that arithmetic progression. For instance, the sequence 5, 7, 9, 11, 13, 15,. .. is an arithmetic progression with a common difference of 2.

$<span class="mw-page-title-main">Egyptian fraction</span> Finite sum of distinct unit fractions$

An Egyptian fraction is a finite sum of distinct unit fractions, such as $That is, each fraction in the expression has a numerator equal to 1 and a denominator that is a positive integer, and all the denominators differ from each other. The value of an expression of this type is a positive rational number ; for instance the Egyptian fraction above sums to . Every positive rational number can be represented by an Egyptian fraction. Sums of this type, and similar sums also including and as summands, were used as a serious notation for rational numbers by the ancient Egyptians, and continued to be used by other civilizations into medieval times. In modern mathematical notation, Egyptian fractions have been superseded by vulgar fractions and decimal notation. However, Egyptian fractions continue to be an object of study in modern number theory and recreational mathematics, as well as in modern historical studies of ancient mathematics.$

The square root of 2 is the positive real number that, when multiplied by itself or squared, equals the number 2. It may be written in mathematics as $or . It is an algebraic number, and therefore not a transcendental number. Technically, it should be called the principal square root of 2, to distinguish it from the negative number with the same property.$

$<span class="mw-page-title-main">Unit fraction</span> One over a whole number$

A unit fraction is a positive fraction with one as its numerator, 1/ $n$ . It is the multiplicative inverse (reciprocal) of the denominator of the fraction, which must be a positive natural number. Examples are 1/1, 1/2, 1/3, 1/4, 1/5, etc. When an object is divided into equal parts, each part is a unit fraction of the whole.

In number theory, natural density, also referred to as asymptotic density or arithmetic density, is one method to measure how "large" a subset of the set of natural numbers is. It relies chiefly on the probability of encountering members of the desired subset when combing through the interval $[1, n]$ as $n$ grows large.

The Erdős–Straus conjecture is an unproven statement in number theory. The conjecture is that, for every integer $that is 2 or more, there exist positive integers , , and for which In other words, the number can be written as a sum of three positive unit fractions.$

In combinatorial mathematics, a large set of positive integers

Erdős' conjecture on arithmetic progressions, often referred to as the Erdős–Turán conjecture, is a conjecture in arithmetic combinatorics. It states that if the sum of the reciprocals of the members of a set A of positive integers diverges, then A contains arbitrarily long arithmetic progressions.

<span class="mw-page-title-main">Sylvester's sequence</span> Doubly exponential integer sequence

In number theory, Sylvester's sequence is an integer sequence in which each term is the product of the previous terms, plus one. Its first few terms are

A geometric progression, also known as a geometric sequence, is a mathematical sequence of non-zero numbers where each term after the first is found by multiplying the previous one by a fixed number called the common ratio. For example, the sequence 2, 6, 18, 54, ... is a geometric progression with a common ratio of 3. Similarly 10, 5, 2.5, 1.25, ... is a geometric sequence with a common ratio of 1/2.

References

↑ Erdős, P. (1932), "Egy Kürschák-féle elemi számelméleti tétel általánosítása" [Generalization of an elementary number-theoretic theorem of Kürschák](PDF), Mat. Fiz. Lapok (in Hungarian), 39: 17–24. As cited by Graham, Ronald L. (2013), "Paul Erdős and Egyptian fractions", Erdős centennial, Bolyai Soc. Math. Stud., vol. 25, János Bolyai Math. Soc., Budapest, pp. 289–309, CiteSeerX 10.1.1.300.91 , doi:10.1007/978-3-642-39286-3_9, ISBN 978-3-642-39285-6, MR 3203600 .
↑ Chapters on the modern geometry of the point, line, and circle, Vol. II by Richard Townsend (1865) p. 24
↑ Modern geometry of the point, straight line, and circle: an elementary treatise by John Alexander Third (1898) p. 44

Mastering Technical Mathematics by Stan Gibilisco, Norman H. Crowhurst, (2007) p. 221
Standard mathematical tables by Chemical Rubber Company (1974) p. 102
Essentials of algebra for secondary schools by Webster Wells (1897) p. 307

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[1] Erdős, P. (1932), "Egy Kürschák-féle elemi számelméleti tétel általánosítása" [Generalization of an elementary number-theoretic theorem of Kürschák](PDF), Mat. Fiz. Lapok (in Hungarian), 39: 17–24. As cited by Graham, Ronald L. (2013), "Paul Erdős and Egyptian fractions", Erdős centennial, Bolyai Soc. Math. Stud., vol. 25, János Bolyai Math. Soc., Budapest, pp. 289–309, CiteSeerX 10.1.1.300.91 , doi:10.1007/978-3-642-39286-3_9, ISBN 978-3-642-39285-6, MR 3203600 .

[2] Chapters on the modern geometry of the point, line, and circle, Vol. II by Richard Townsend (1865) p. 24

[3] Modern geometry of the point, straight line, and circle: an elementary treatise by John Alexander Third (1898) p. 44

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