More very interesting numbers | The game of science | EUROtoday

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To the record of very interesting points from final week, we might add some extra prompt by our astute readers. In growing order, they’re: 1,618… (the golden ratio), 5, 8, 9, 10, 113 and 6174.

But earlier than giving these candidates to seem within the record of probably the most interesting numbers the eye they deserve, let us take a look at the ingenious demonstration that led the Pythagoreans to conclude that √2 couldn’t be a rational quantity, that’s, expressible by a fraction. :

Suppose that this fraction exists and that, subsequently, √2 = a/b, the place a and b are usually not each even (as a result of in the event that they had been each even, we might simplify the fraction by dividing the numerator and denominator by 2 a number of instances).

Squaring the 2 members of the equality:

2 = a2/b2, then do not:

2b2 = a2, so a2 is even, and subsequently a is even (for the reason that sq. of an odd quantity is at all times odd), then

a = 2n, the place n is an integer, then

a2 = 4n2, so

b2 = 2n2, so b2 is even and so is b, opposite to the beginning premise, in line with which a and b are usually not each even. Therefore, the supposed fraction equal to √2 is inconceivable.

And let’s go together with the brand new candidates for very interesting numbers:


The golden ratio, Φ = 1.618…, along with its aesthetic significance, is expounded to the Fibonacci sequence (a relationship that we have now handled occasionally) and has interesting arithmetic and geometric properties. It is one of the few irrational numbers that, like π ye, has its personal title; however it’s not transcendent, like these two, however algebraic. Can you discover the quadratic equation of which it’s the answer?


There are 5 Platonic solids (common polyhedra). It is a Pythagorean cousin: 52 = 22 + 12, in addition to the hypotenuse of the “golden triangle”, with legs 3, 4 and 5. It is the quantity of fingers on a human hand, which is why we use a numbering system of base 10. Can you suppose of another notable traits of the quantity 5?


In addition to turning into, when knocked down, the image of infinity, it’s the smallest good dice (not counting the trivial case of 1), and, talking of cubes, the quantity of vertices of the hexahedron. It can be a cake quantity, sensible, refactorable…

In addition to being very interesting individually, 5 and eight are additionally very interesting as a pair, since 8/5 = 1.6 is an effective approximation to Φ, the golden ratio.


Mariana Días finds the 9 very geometric (why?). Furthermore, 9 is an autonumber, it’s a refactorable quantity, a Motzkin quantity, a Kaprekar quantity, a Padovan quantity, it’s an exponential factorial…


It is the idea of our numbering system, which might be sufficient to incorporate it in any record of very interesting numbers. Plus, it is a Harshad quantity, a Perrin quantity, a Stormer quantity… And it is a completely satisfied quantity.


Our common commentator Rafael Granero proposes 113 as it’s the smallest three-digit Wednesday quantity. A Wednesday quantity is a chief quantity the place any two consecutive digits type a chief, and all these primes fashioned are completely different (for instance, 13171, since 13, 31, 17 and 71 are all primes).

The query -says Granero- is what’s the largest cousin Wednesday quantity that exists?


Fernando Garro loves 6174, often called “Kaprekar’s constant”, a “magic” quantity that, after a collection of repetitive operations primarily based on any four-digit quantity, at all times finally ends up showing. But that is one other article.

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