Add 13 more and post it forever.

bobbym · 2010-05-21 21:36:14

6513 = 5 * 13 = 65

phrontister · 2010-05-21 22:07:45

Hey, ZHero! Did Joan change her phone number from a 6-digit positive one to an 8-digit negative one?!! She didn't tell me!

bobbym · 2010-05-21 22:12:47

6539

6,5,3,9 first appears at positions:

ZHero · 2010-05-21 22:27:01

phrontister wrote:

Hey, ZHero! Did Joan change her phone number from a 6-digit positive one to an 8-digit negative one?!! She didn't tell me!

Ooops! One of the powers needed a fix...
(1×3)[sup]1+3+3+1[/sup] → (1×3)[sup]1×3+3×1[/sup]
Done that!!!

And i'll ask J to keep that number forever... Its propitious.

ZHero · 2010-05-21 23:37:27

6542 =

6565 = 5 × 13 × 101 = (1×3×1)[sup]1+3+3+1[/sup] + 3 + 1

513101 is a Prime number.

135101 is a Prime number.

101513 is a Prime number.

phrontister · 2010-05-22 00:25:00

ZHero wrote:

6542 =

*Ahem* ->

bobbym · 2010-05-22 00:36:38

6591

ZHero · 2010-05-24 22:48:21

6617 ← ketchdown

6617+617+17+7-11 is a Prime number.

6617+617+17+7-131 is a Prime number.

6617+617+17+7-1331 is a Prime number.

Last edited by ZHero (2010-05-25 03:22:40)

ZHero · 2010-05-24 22:49:24

6604 ← cetchup

6604+604+04+4+13 is a Prime number.

6604+604+04+4+13131313 is a Prime number.

6604+604+04+4+31 is a Prime number.

6604+604+04+4+31313131 is a Prime number.

Last edited by ZHero (2010-05-24 23:52:56)

phrontister · 2010-05-25 03:10:53

bobbym · 2010-05-25 03:51:40

6643

phrontister · 2010-05-25 04:01:21

How on earth did you do that?! :)

Btw, my calculator gives the same result.

Oh...I just noticed you did the same thing back in post #496. But I didn't think then about how you might have done it.

When John Franklin started this thread I thought it would get boring and would soon fizzle, but 2^9x13 posts later, with lots of very interesting contributions, and we're still going!

Last edited by phrontister (2010-05-25 04:22:43)

ZHero · 2010-05-25 04:23:31

6669 ←

bobbym · 2010-05-25 18:02:49

6682 first appears at:

How on earth did you do that?!

I see, buttering me up with flattery for the kill. You will quickly figure it out, of that I am sure.

phrontister · 2010-05-27 03:35:50

Last edited by phrontister (2010-05-27 03:42:27)

bobbym · 2010-05-27 03:45:01

The string 6708 first appears at:

phrontister · 2010-05-27 04:12:07

Trying out the new toy again.

bobbym · 2010-05-27 04:19:59

6734

(6 + 7)(4-3) = 13

phrontister · 2010-05-27 05:42:18

Last edited by phrontister (2010-05-27 06:25:34)

bobbym · 2010-05-27 06:21:30

Pleasant dreams.

6760 = 6 + 7 + ( 6 * 0 ) = 13

Your code is nicely written and I believe considerably faster than mine. This is a case where the functional and rule based progamming style that I have used is slower than the procedural approach that you have taken. I believe the problem is in the RealDigit command. Built in but still too slow. I can see some obvious improvements, that should speed it up.

phrontister · 2010-05-27 12:00:34

G'mornin', Bobby! That was a mighty short night...and you're to blame! But it was all good fun, so thanks for making me do it!

Yes, your code runs much slower than mine...and it also has that extra step. You may have omitted something from it, too, because with the two test numbers I tried it on the result was one less than the correct answer. I still haven't worked out yet what yours does because of the strange (to me) terms. I don't have a rule-based programming-style bone in my body...I began with a basic idea and then had to consult M's excellent help pages to overcome each obstacle (there were several!) with a function that did the trick.

One downside of mine is that it 'runs' like it's wading through molasses for digit precision greater than 10,000. I tried it with 50,000 (or was it 20,000?...can't remember), and it slowed down to an absolute crawl! Maybe yours doesn't have that problem.

I'll run my code again for this post to make sure it wasn't all a dream!

EDIT: I got a 13% speed increase just now by removing StringReplace and increasing the start and end positions by one (StringReplace was there to eliminate the decimal point for the digit count). And it trims the code down, too.

Last edited by phrontister (2010-05-27 12:56:07)

bobbym · 2010-05-27 13:07:59

6786 = 6 + 6 + ( 8 - 7 ) = 13

I am working on something that should be faster. Functional or rule based are the preferred paradigms for M. Loosely explained it means pure functions and no for, do , or while loops.

The reason for 1 more is because I count the integer digit up front. 1.342627645. 7645 occurs at position 7.

Phrontister;

With your permission, I will ask MIF that you are elevated to Real Member. If you would ask I know he would grant it. If you are too busy I will be glad to ask for you.

ZHero · 2010-05-27 22:44:14

6799 = 313 + 131 + 31 + 13 + 33 + 1 + 1

6 + 7 + 9 - 9 = 13

6 + 7 + 9 + 9 = 31

670099 is a Prime number.

6790009 is a Prime number.

67900009 is a Prime number.

60000799 is a Prime number.

60700909 is a Prime number.

600007009009 is a Prime number.

600000000799 is a Prime number.

6000070000090009 is a Prime number.

phrontister · 2010-05-28 03:33:08

Oops! I used this post as a template for my post #534 and pressed Submit, thereby deleting my original post! Grrrr

I think it went something like this:

Hi Bobby,

I've asked MathsIsFun if my member status could be downgraded to Real Member. Haven't heard back yet.

I don't recall the maths part, so I'll use this:

Last edited by phrontister (2010-05-29 13:41:04)

bobbym · 2010-05-28 03:48:48

6825

Hi phrontister;

Yes, I know, it may take a little time. Also it is not downgrading. It gives you an extra privilege. But if you really don't want that, feel free to remove your request. I thought it would be a good idea so that we could PM small code snippets without cluttering up the posts. You may not agree.

Math Is Fun Forum

#501 2010-05-21 21:36:14

Re: Add 13 more and post it forever.

#502 2010-05-21 22:07:45

Re: Add 13 more and post it forever.

#503 2010-05-21 22:12:47

Re: Add 13 more and post it forever.

#504 2010-05-21 22:27:01

Re: Add 13 more and post it forever.

#505 2010-05-21 23:37:27

Re: Add 13 more and post it forever.

#506 2010-05-22 00:25:00

Re: Add 13 more and post it forever.

#507 2010-05-22 00:36:38

Re: Add 13 more and post it forever.

#508 2010-05-24 22:48:21

Re: Add 13 more and post it forever.

#509 2010-05-24 22:49:24

Re: Add 13 more and post it forever.

#510 2010-05-25 03:10:53

Re: Add 13 more and post it forever.

#511 2010-05-25 03:51:40

Re: Add 13 more and post it forever.

#512 2010-05-25 04:01:21

Re: Add 13 more and post it forever.

#513 2010-05-25 04:23:31

Re: Add 13 more and post it forever.

#514 2010-05-25 18:02:49

Re: Add 13 more and post it forever.

#515 2010-05-27 03:35:50

Re: Add 13 more and post it forever.

#516 2010-05-27 03:45:01

Re: Add 13 more and post it forever.

#517 2010-05-27 04:12:07

Re: Add 13 more and post it forever.

#518 2010-05-27 04:19:59

Re: Add 13 more and post it forever.

#519 2010-05-27 05:42:18

Re: Add 13 more and post it forever.

#520 2010-05-27 06:21:30

Re: Add 13 more and post it forever.

#521 2010-05-27 12:00:34

Re: Add 13 more and post it forever.

#522 2010-05-27 13:07:59

Re: Add 13 more and post it forever.

#523 2010-05-27 22:44:14

Re: Add 13 more and post it forever.

#524 2010-05-28 03:33:08

Re: Add 13 more and post it forever.

#525 2010-05-28 03:48:48

Re: Add 13 more and post it forever.

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