Charles 3781

9 hours ago, Sensei said:

Yesterday, it was too late. OK. Now, I made program in C/C++:

#include <stdio.h>

//int primes[] = { 2, 3, 5, -1 };
int primes[] = { 2, 3, 5, 7, 11, 13, 17, 19, 23, -1 };

bool check(int a, int b) {
	for (int i = 0; primes[i] > 0; i++) {
		if ((a % primes[i]) == 0) return(false);
		if ((b % primes[i]) == 0) return(false);
	}
	return(true);
}

int main(int argc, int *argv[]) {
	int count = 0;
	int end = 1;
	printf("Primes: ");
	for (int i = 0; primes[i] > 0; i++) {
		printf("%d ", primes[i]);
		end *= primes[i];
	}
	printf("\n");
	printf("End %d\n", end);
	int half = end / 2;
	for (int i = 0; i < half; i++) {
		int a = i;
		int b = end - a;
		if (check(a, b)) {
			//printf("Found %d %d\n", a, b);
			count++;
		}
	}
	printf("Count %d\n", count);
	return(0);
}

For test case with 3 primes it gave:

Which looks good.

For OP problem with 9 primes it gave too many results to show them all (so had to disable printf()):

18 mln is over twice more than OP value.

Could you translate your program into BASIC, please, as that's the only programming language I understand?

16 hours ago, VenusPrincess said:

If you told me the average temperature on the Martian surface was -60 °C that would be utterly useless for our efforts to engineer a rover to survive on Mars. A useful understanding of the thermodynamics of planet's atmosphere simply cannot be summarized in a single number. It contains very little useful information.

Surely, you are going too far.  If we know that the average temperature of the Martian surface is -60C, how can that be "utterly useless" in our efforts to engineer a rover capable of surviving on Mars?  On the contrary, it has enabled us to engineer numerous recent examples of rovers capable of operating in this low-temperature Martian environment.  

11 minutes ago, swansont said:

Whichever one you want it to. You can choose your own coordinate system. You want that to be the z direction, it can be z. If you want it to be y, it can be y. You can call it the first, second or third dimension. It won’t affect the physics.

(coordinate system choice will affect how hard it is to solve a physics problem, though)

I hope that when you get on a plane, your pilot doesn't follow the same objective scientific approach to co-ordinate system choice, when landing

28 minutes ago, zapatos said:

I'd like to say goodbye now in case I'm not here when you are shown the door.

We door-spiders pop up to catch our prey again.

12 minutes ago, Phi for All said:

I think you enjoy being in the dark more than spiders.

Crikey, I'm not sure what that means, Phi - will you semaphore it by waving your spinnarettes at me on the Dark web, if you get my drift. Nudge, nudge.

Just now, CuriosOne said:

So the 3rd dimension is an illusion?

No,  it's real, but we can only visually perceive its reality because we  have two eyes.  If we were one-eyed creatures like a Cyclops, we'd see everything as optically flat and 2-dimensional.

We'd have to use our hands and possibly other appendages, to feel the three-dimensional physicality of bodies.

I would say, that for humans, the 3rd dimension is "depth" . Like when we look at the colourful images which you kindly posted, in your OP. 

These are attractive, but exist only on our screens, in the form of flat 2-dimensional images.

If we could perceive them in 3 dimensions as solid objects, we would be able to truly visual their 3rd dimensional nature.

5 minutes ago, John Cuthber said:

No it isn't.
I'm OK with them. Some people keep them as pets.
 

I don't believe you keep a spider as a pet.  Or actually know, or ever met  anyone who does.  I bet you just read about the idea in a book, didn't you?

On 3/24/2020 at 10:24 PM, Michael McMahon said:

https://theconversation.com/explainer-why-are-we-afraid-of-spiders-26405

I’ve been wondering a small bit about the irrational fear evoked by spiders and snakes. Some people say there may be an evolutionary component to it as a few of these creatures can potentially be deadly. But our visceral response to them seems to be far more excessive than the actual threat they would have posed throughout human evolution.

 

Humans obviously have a limited capacity to empathise with animals. We can anthropomorphise our pets and we might admire animals in the zoo. But as the philosopher Thomas Nagal pointed out, “What is it Like to be a Bat?”. In other words what is the sentience of these creatures like?

 

They can’t just be inanimate robots as they display complex behaviour. Perhaps they live in a barely self-aware oneiric sort of existence that will be forever unknown to us. Some exotic creatures may possess a mind so “alien” to ours that it becomes repulsive when we try to project a degree of consciousness onto it. So might the creepiness of spiders and snakes be more of our instinctive reaction to their unfathomable psychology rather than the actual biology of them?

Snakes have never bothered me.  But I absolutely can't stand spiders.  They're so frightening, with their multiple, thin, stalky legs and unnaturally fast rushing mechanical movements.

This fear and loathing of spiders seems universal in humans.  I once read in a book, that it is caused by spiders being of extra-terrestrial origin.  Could that be true?

Isn't the point of calculus this  -  only proper mathematicians can understand it.

Just now, Kartazion said:

According to many people, the whole universe was born from nothing.

Don't you mean, "according to scientists", the whole Universe was born from nothing?    

Suppose you were asked, "Where did your  computer come from?"  And you said:  "That's a meaningless question - it came from nothing."   How would you respond?

According to current theory, didn't the entire Universe spring from a minute "Black Hole" smaller than a proton. Then expanded outwards. To create trillions of stars, galaxies and so on.

Given the wide vista of prospects allowed by such a theory,  would you rule anything at all out,  as physically impossible?

Just now, jdla22 said:

Nonsense! I thought it was a rather interesting addition. You never know what something off-topic will inspire.

Well of course it was.  But please understand my position.  When one has acquired a -25 rating,  and  faces the danger of getting booted off,  a degree of unctuousness is called for.

You're right. My post was definitely off-topic, Apologies for derailing the thread.

4 minutes ago, Dord said:

 

There's a (fairly) famous quote from poem The Rhyme of the Ancient Mariner by Samuel Coleridge that emphasises this very point...

"Water, water, every where, nor a drop to drink."

https://www.poetryfoundation.org/poems/43997/the-rime-of-the-ancient-mariner-text-of-1834

(Although the modern version has not instead of the outdated nor.)

 

Thanks Dord.  On your remark concerning the outdated "nor",  I think  you raise a valuable point.

Consider these two lines:

"Water, water, everywhere, nor any drop to drink" -  (18th century original)

"Water, water, everywhere, and not a drop to drink" - (revised 21st century modern)

The modern revision gets rid of the awkward " nor".  Replacing it by the much smoother, and  more natural "and not".  A definite literary  improvement.

In a similar way, Science is always being revised and improved.  For example we have improved our understanding of combustion,  by replacing the 18th century  "phlogiston",  with "oxidation".  Shouldn't such scientific principles  be applied to past literature,  so as to update and improve it.

Science and Religion are both attempts to make sense of the world.  For that, they both deserve praise and credit.  Humans like to make sense of things. 

But isn't the essential difference between Science and Religion this  -  Science employs mathematics.  This is seen In any book of Science.  Whether the book is about Physics, Chemistry, Biology, Geology, Sociology,  or any other scientific study.  Always,  in the book,  you will find maths.  In the form of precise numerical data, detailed tables of figures, . Which prove, or at least lend substantial credibility to,  the assertions made in the book.

But is this case with religious books, such as the Bible.  Are there any mathematical  data contained in the Bible, which enhance its credibility?

5 minutes ago, swansont said:

No, not if it’s seawater, or of similar salinity

”Human kidneys can only make urine that is less salty than salt water. Therefore, to get rid of all the excess salt taken in by drinking seawater, you have to urinate more water than you drank. Eventually, you die of dehydration even as you become thirstier.”

https://oceanservice.noaa.gov/facts/drinksw.html

Thanks swansont for clarifying that point.  I used to wonder how sailors could die in agony of thirst when surrounded by water.  I thought: "Well, even if the sea-water has got salt in it, surely a little bit of it,  would at least help relieve the thirst".  And you know -  I still kind of think that way!  But, as you explain in your post, both science and maritime experience testify to the contrary.  From the point of view of long-term survival, that is.

If you were dying of thirst, wouldn't sipping salt-water in modest quantities relieve dehydration?

We live on a planet which has ~70% of its surface covered by oceans with an average depth of~ 12,000 ft  of water. 

Given these facts, doesn't it seem strange that we're worried about water-shortage?

I wouldn't get too excited about marginal instrument readings from a distant planet such as Venus.

This has happened before, in the case of the similarly distant planet Mars.  You know what I mean - the "canals".

1 minute ago, Strange said:

I would say someone capable of critical thinking, who asks probing questions, who thinks about the meaning of the words used, etc.

They don't have to have any big ideas, just able to analyse ideas.

Well perhaps. But  we've had 2,000 years of philosophers.  Like Plato and Aristotle.  Aristotle analysed ideas.   He came up with the conclusion that everything below the Moon is made of four elements:

1. Earth

2. Air

3. Fire

4.Water

And everything above the Moon is made of a luminous 5th element.

This was so ridiculous, that it got protested against even by contemporary Ancient Greek scholars.  Unfortunately, their voices were drowned by Aristotle's philosophical followers, who established a reign of scientific terror that lasted 1,500 years.

Isn't that what philosophers are.  They can't do maths, don't know anything useful.  They just waffle and bluff.  Or have they any redeeming features.

How would you define someone who claims to be a "Philosopher?

Is it someone who has big ideas, and would really like to be a Physicist.

But can't do the maths.

Thanks Enthalpy.  You show very clearly, the scientific principles which ought to influence the design of musical instruments, so that they work most effectively.

Isn't it a pity that traditional instruments haven't been designed along these scientific lines.  Rather, the instruments seem to have evolved in a kind of haphazard way.

For example, we  have, nowadays, all kinds of "wind" instruments, such as the trumpet , bugle, flute, clarinet and recorder.  And stringed instruments like the banjo, violin, cello, and double bass.  Do we need all these different instruments?  Couldn't they be scientifically reduced to a single all -purpose instrument .

Just as past  key-board instruments like the clavichord and harpsichord, have been perfected into the modern piano?