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2010-09-03, 13:41   #23
Mini-Geek
Account Deleted

"Tim Sorbera"
Aug 2006
San Antonio, TX USA

102668 Posts

Quote:
 Originally Posted by 3.14159 How about 77? 49? (7 * 11 and 72)
While it's subjective, I'd say these are much easier to spot as composite than 91, since one is a multiple of 11, and the other is a square. 91, on the other hand, is 7 times a prime greater than 10 that doesn't produce a clearly-visible way to identify it (e.g. with 11 times a single digit both digits are the same, and with 3 you can see that the digits add to a multiple of 3, but to see 91=7*13 I'd have to break it as 70+21 and then see that 21 is a multiple of 7).

Last fiddled with by Mini-Geek on 2010-09-03 at 13:44

2010-09-03, 14:13   #24
R.D. Silverman

"Bob Silverman"
Nov 2003
North of Boston

23×3×311 Posts

Quote:
 Originally Posted by Mini-Geek While it's subjective, I'd say these are much easier to spot as composite than 91, since one is a multiple of 11, and the other is a square. 91, on the other hand, is 7 times a prime greater than 10 that doesn't produce a clearly-visible way to identify it (e.g. with 11 times a single digit both digits are the same, and with 3 you can see that the digits add to a multiple of 3, but to see 91=7*13 I'd have to break it as 70+21 and then see that 21 is a multiple of 7).
As much as I hate to enter a conversation in which pi-man and science_man
are participating, I do have something material to add here.

Look up the paper by Selfridge et.al. entitled "Primes at a Glance"

2010-09-03, 17:31   #25
davieddy

"Lucan"
Dec 2006
England

2×3×13×83 Posts

Quote:
 Originally Posted by R.D. Silverman As much as I hate to enter a conversation in which pi-man and science_man are participating, I do have something material to add here. Look up the paper by Selfridge et.al. entitled "Primes at a Glance"
As much as I hate to enter a conversation in which math-man is
participating, will he agree that the first uninteresting number is
greater than 91?

David

 2010-09-03, 17:55 #26 CRGreathouse     Aug 2006 3·1,993 Posts Please be kind. R. D. Silverman's recommendation is excellent. I might also mention the Agoh-Erdős-Granville followup paper "Primes at a (somewhat lengthy) glance", probably one of the last papers Erdős wrote.
2010-09-04, 00:01   #27
davieddy

"Lucan"
Dec 2006
England

647410 Posts

Quote:
 Originally Posted by CRGreathouse Please be kind.
Hmm.

I thought quoting the great man verbatim was cutting
but appropriate and witty. If he is that thin-skinned, he should
moderate his own tone. I was merely attempting to console the
targets of his original jibe.

I'm sure his and your recommendations are valuable, enjoyable
and maybe even readable

David

2010-09-04, 02:10   #28
3.14159

May 2010
Prime hunting commission.

24·3·5·7 Posts

Quote:
 Originally Posted by Charles Please be kind. R. D. Silverman's recommendation is excellent. I might also mention the Agoh-Erdős-Granville followup paper "Primes at a (somewhat lengthy) glance", probably one of the last papers Erdős wrote.
I'm never going to be kind to low-down internet narcissists who pretends to know everything. Never will.

Quote:
 Originally Posted by David I thought quoting the great man verbatim was cutting but appropriate and witty. If he is that thin-skinned, he should moderate his own tone. I was merely attempting to console the targets of his original jibe.
Expecting moderation from a narcissist is expecting the moon to be made of cheese.

Last fiddled with by 3.14159 on 2010-09-04 at 02:15

2010-09-04, 04:21   #29
CRGreathouse

Aug 2006

3×1,993 Posts

Quote:
 Originally Posted by davieddy I'm sure his and your recommendations are valuable, enjoyable and maybe even readable
Eminently readable, actually! Possibly even by an undergraduate.

2010-09-04, 04:53   #30
3.14159

May 2010
Prime hunting commission.

24×3×5×7 Posts

Quote:
 Originally Posted by Charles Eminently readable, actually! Possibly even by an undergraduate.
Excellent.

Last fiddled with by 3.14159 on 2010-09-04 at 04:54

2010-09-04, 13:21   #31
davieddy

"Lucan"
Dec 2006
England

145128 Posts

Quote:
 Originally Posted by CRGreathouse Eminently readable, actually! Possibly even by an undergraduate.
What about a senile half-blind alcoholic?

David

2010-09-04, 13:26   #32
davieddy

"Lucan"
Dec 2006
England

2×3×13×83 Posts

Quote:
 Originally Posted by 3.14159 I'm never going to be kind to low-down internet narcissists who pretends to know everything. Never will. Expecting moderation from a narcissist is expecting the moon to be made of cheese.
Narcissus is a bit archaic.
I believe the current parlance is "head up one's arse".

David

2010-09-04, 14:12   #33
3.14159

May 2010
Prime hunting commission.

24·3·5·7 Posts

Quote:
 Originally Posted by David What about a senile half-blind alcoholic?
Depends on whether or not he is intoxicated.

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