# The Grey Labyrinth is a collection of puzzles, riddles, mind games, paradoxes and other intellectually challenging diversions. Related topics: puzzle games, logic puzzles, lateral thinking puzzles, philosophy, mind benders, brain teasers, word problems, conundrums, 3d puzzles, spatial reasoning, intelligence tests, mathematical diversions, paradoxes, physics problems, reasoning, math, science.

Author Message
Jingle47
Daedalian Member

 Posted: Tue Apr 16, 2002 4:33 am    Post subject: 1 I am doing a little digging and am working with prime factorizations. What I reall want to know is how YOU figure out if the following number is prime. 100000000000000000207 I actually already know whether it is prime or not, I am more interested in your approach(es). I would appreciate any help I can get and who knows you might find it fun to do anyway!
Chuck
Daedalian Member

 Posted: Tue Apr 16, 2002 7:09 am    Post subject: 2 I used a program called PRNTEST1.UB that came with the UBasic programming language that I found online somewhere months ago. I don't know how it works. It says 100,000,000,000,000,000,207 is prime.
ctrlaltdel
Member of the Daedalians

 Posted: Tue Apr 16, 2002 7:37 am    Post subject: 3 is there a way 'around' the problem? say i look at the big number and say: 207 is not a prime, 207 = 23 x 3 x 3 now if 10000000000000000000 is divisible by either 23 or 3 then the whole number is not a prime if its not tho... then i guess i don't know yet anyways an approach like this maybe totally misleading only because of the bunch of zeros i try to enforce it on the problem. if the number was something like 13215746545135464316545207 i'd be stuck with the brute force efforts. [This message has been edited by ctrlaltdel (edited 04-16-2002 03:39 AM).]
groza528
No Place Like Home

 Posted: Tue Apr 16, 2002 7:55 am    Post subject: 4 It may be a difference of two squares, in which case it is not prime. That's probably the first thing I'd check is what's the next square, and then find the difference between the two. Unfortunately I'm too lazy to do that. Is that supposed to be ...00207 or ...027?
groza528
No Place Like Home

 Posted: Tue Apr 16, 2002 7:55 am    Post subject: 5 If ...027 there's probably a difference of two cubes formula
mole
Subterranean Member

 Posted: Tue Apr 16, 2002 9:21 am    Post subject: 6 13215746545135464316545207 is not prime.
CrystyB
Misunderstood Guy

 Posted: Tue Apr 16, 2002 10:19 pm    Post subject: 7 Groza, except 10^20 is not a cube
Quailman
His Postmajesty

 Posted: Tue Apr 16, 2002 10:26 pm    Post subject: 8 If it had nine or fewer digits, I would look here.
CzarJ
Hot babe

 Posted: Wed Apr 17, 2002 1:38 am    Post subject: 9 Oh, I read about stuff like this in a book! I don't really understand how it works, though ------------------ Speaking of which, describe your favorite pair of pants.
Jingle47
Daedalian Member

 Posted: Wed Apr 17, 2002 5:01 am    Post subject: 10 I found out the answer using a program called Maple 6. But I am kind of curious how Maple found the answer.
SaberKitty
one can always be hopeful...

 Posted: Wed Apr 17, 2002 5:06 am    Post subject: 11 I don't knwo the answer, but I just wanted to post this site because it's really cool The Great Internet Mersenne Prime Search(GIMPS Homepage) -admits she's a geek -
Griffin
Daedalian Member

 Posted: Wed Apr 17, 2002 8:30 pm    Post subject: 12 Jingle - It probably used one of the "primality tests" found at this site: http://www.utm.edu/research/primes/prove/proving.html
jamesshuang
Icarian Member

 Posted: Tue Apr 23, 2002 7:15 pm    Post subject: 13 TI-89 calculators rule. They are great for finding primes. 100000000000000000207 is actually prime, by the way.
extropalopakettle
No offense, but....

 Posted: Thu Apr 25, 2002 2:29 am    Post subject: 14 Here's a java program to test if any integer is prime or not: code: import java.math.BigInteger; class testPrime { public static void main(String[] args) { BigInteger n = new BigInteger(args[0]); if (n.isProbablePrime(30)) System.out.println("PRIME"); else System.out.println("COMPOSITE"); } } The constant 30 can be changed. The higher it is, the less likely it is you'll get a false positive (positive=prime). You'll never get a false negative. For a value of X, the probability that a positive result is false is less than 1/2^X.
 Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year by All usersChuckCrystyBctrlaltdelCzarJextropalopakettleGriffingroza528jamesshuangJingle47moleQuailmanSaberKitty Oldest FirstNewest First
 All times are GMT Page 1 of 1

 Jump to: Select a forum Puzzles and Games----------------Grey Labyrinth PuzzlesVisitor Submitted PuzzlesVisitor GamesMafia Games Miscellaneous----------------Off-TopicVisitor Submitted NewsScience, Art, and CulturePoll Tournaments Administration----------------Grey Labyrinth NewsFeature Requests / Site Problems
You cannot post new topics in this forum
You can reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum