From Lee Sallows:
“The above three strips of ten numbers have an intriguing property. They record how many times each of the decimal digits (shown at left) occur in the other two strips. Hence the 6 in the left-hand strip identifies the number of 0’s in strips B and C, while the 2 in the centre strip counts the number of 3’s present in strips A and C. Moreover, the same property holds for every number in all three strips.”
See Reciprocation.
(Thanks, Lee.)
Say what you will about hell, it’s very well organized. According to the 17th-century grimoire Ars Goetia, the underworld is ruled by 72 demons, each with its own sigil (above) and served by a sort of infernal bureaucracy:
Aim (also Aym or Haborym) is a Great Duke of Hell, very strong, and rules over twenty-six legions of demons. He sets cities, castles and great places on fire, makes men witty in all ways, and gives true answers concerning private matters. He is depicted as a man (handsome to some sources), but with three heads, one of a serpent, the second of a man, and the third of a cat to most authors, although some say of a calf, riding a viper, and carrying in his hand a lit firebrand with which he sets the requested things on fire.
Wikipedia has a page explaining who does what.
Related: Belphegor’s prime, 1000000000000066600000000000001, is a palindromic prime number with 666 at its heart and 13 zeros on either side. It was discovered by Harvey Dubner; Clifford Pickover named it after a prince of hell responsible for helping people make ingenious inventions and discoveries.
A popular mathematical puzzle asks: Suppose Earth were perfectly spherical and wrapped with a string at the equator. If we wanted to raise the string 1 meter off the ground, all around the world, how much longer would it need to be?
Surprisingly, the answer is only about 6.3 meters. A circle of radius r has a circumference of 2πr. We’re adding a meter to the radius, so the circumference increases by 2π meters.
Even more remarkably, this remains true regardless of the size of the sphere. Above, the increase in the circumference (blue) remains the same for a sphere of any size — it’s determined entirely by the additional radius (red).
The shape need not even be a sphere! Below, when the string is raised one meter (red) outward from the perimeter of either square, the string’s total length increases only by the combined length of the four blue arcs, which together equal the circumference of a circle of radius 1, or 2π meters.
The infinite monkey theorem holds that a monkey typing at random for an infinite amount of time will almost certainly produce the works of Shakespeare.
This may be true, but mathematicians Stephen Woodcock and Jay Falletta of the University of Technology Sydney find that it would take an extraordinarily long time — longer, in fact, than the life span of the universe.
Assuming a typing speed of one character per second on a 30-key keyboard, they find, a single chimp has only about a 5 percent chance of typing BANANAS in its own lifetime. And even the entire global population of 200,000 chimps will almost certainly never string together the 884,647 words that make up Shakespeare’s works within 10100 years.
“There are many orders of magnitude difference between the expected numbers of keys to be randomly pressed before Shakespeare’s works are reproduced and the number of keystrokes until the universe collapses into thermodynamic equilibrium,” the authors conclude. “As such, we reject the conclusions from the Infinite Monkeys Theorem as potentially misleading within our finite universe.”
Speaking of Shakespeare: Grand Theft Hamlet is a British documentary about the staging of a production of Hamlet inside Grand Theft Auto:
Winner of the Jury Award for best documentary feature at the 2024 SXSW Film Festival, it will be released in the U.K. in December and globally early next year.
(Thanks, John.)
The least knotted of all knots is a simple closed loop, the “unknot.” Certainly this is easy to spot on its own, but adding even a few twists can make it hard to recognize:
An elaborately draped loop can be quite difficult to distinguish from a knottier knot. Is this an unknot?
(Yes, it is.)
Surprisingly, while research is ongoing, it remains unknown whether the challenge of recognizing unknots is efficiently solvable — whether an algorithm can accomplish the task in polynomial time. It’s an open question.
In the 18th century Leonhard Euler famously addressed the question whether it was possible to walk through the city of Königsberg and return to one’s home having crossed each of seven bridges exactly once.
The answer, briefly, was no, but in 2013 network scientist Thilo Gross noticed that the city of Bristol has a similar layout, and here the task is possible: If you’re willing to walk 30 miles, you can cross each of the 45 bridges on this map and return to your starting point.
A paradox by Columbia University logician Haim Gaifman:
line 1: The sentence on line 1 is not true.
line 2: The sentence on line 1 is not true.
line 3: The sentence on line 2 is not true.
line 4: The sentence on line 3 is not true.
line n + 1: The sentence on line n is not true.
All these sentence are equivalent, because each essentially restates its predecessor. Since the sentence on line 1 isn’t true, the sentence on line 3 isn’t true either. “[B]ut what I have just stated is not true, because it is the sentence on line 4 (or an obviously equivalent reformulation of it), and also this last statement of mine is not true, because it is the sentence on line 5, etc. None of these sentences can be successfully asserted, because none of them is true; but again I find myself slipping into nontruth: what I have just said is not true for it obviously includes the conjunction of these very same sentences; and also this last assertion is not true, and so on ad infinitum.”
(Haim Gaifman, “Pointers to Truth,” Journal of Philosophy 89:5 [May 1992], 223-261. See Yablo’s Paradox.)
10/22/2024 UPDATE: Interesting addendum from reader Mark Thompson: The capital cities Asunción, Canberra, and Kuwait City are nearly equidistant on great-circle routes:
Kuwait City to Canberra: 12,768 km
Canberra to Asunción: 12,712 km
Asunción to Kuwait City: 12,766 km
“Their mutual distances apart (along the earth’s surface) happen to be very close to one Earth-diameter [12,742 km]: so, sadly, they don’t all lie on a single great circle (since pi is not 3).” (Thanks, Mark.)
Ghost leg is a method of establishing random pairings between any two sets of equal size. For example, it might be used to assign chores randomly to a group of people. The names of the participants are listed across the top of the diagram and the chores across the bottom, and a vertical line is drawn connecting each name to the chore below it. Then the names are concealed and each participant adds a “leg” to the diagram. A leg is a segment that connects two adjacent vertical lines (it must not touch any other horizontal line).
When the legs have been drawn, the names are revealed and a path drawn from each name to the bottom of the diagram. Each path must follow each leg that it encounters, jumping to the adjacent vertical line and continuing downward. When it reaches a chore at the bottom, it establishes a link between a name and a chore.
The benefit of this method is that it will work for groups of any size, reliably establishing a 1:1 correspondence between their elements. And it will work no matter how many horizontal lines are added. In Japanese it’s known as amidakuji.
From Lee Sallows:
A feature common to many geomagic squares is that the set of shapes they employ reveal an atomic structure. That is, they are built up from repeated copies of a single unit shape. Examples of this are piece sets composed of polyominoes, the unit shape then being a (relatively small) square.
For the would-be geomagic square constructor, a key advantage of the atomic property is that the shapes concerned are each describable in terms of the positions of their constituent atoms. Or, to put it another way, they can be represented by a set of numbers. Hence, unlike non-atomic shapes, they are readily amenable to analysis and manipulation by computer.
Take, for example, an algorithm able to identify and list each of the different ways in which a given planar shape can be tiled by some specified set of smaller shapes. Such a program might be challenging to write, but provided the pieces concerned are composed of repeated units, implementation ought to be straightforward. But could the same be said in the case of non-atomic pieces? Without a set of numbers to describe piece shapes, how are they to be represented in a digital computer?
This is worth noting since, as inspection will show, the shapes employed in the square above are plainly non-atomic. In line with this I can confirm that the only computer program involved in deriving this solution was a vector graphics editor used to create the drawing seen above.
(Thanks, Lee.)
