# Code Busters: Guess my PIN
**URL:** https://boards.straightdope.com/t/code-busters-guess-my-pin/200908
**Category:** Miscellaneous and Personal Stuff I Must Share
**Created:** [September 11, 2003, 3:41am UTC](https://boards.straightdope.com/t/code-busters-guess-my-pin/200908 "2003-09-11T03:41:46Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@Blown\_Injected](https://boards.straightdope.com/u/Blown_Injected)
#### Post date: [September 11, 2003, 3:41am UTC](https://boards.straightdope.com/t/code-busters-guess-my-pin/200908/1 "2003-09-11T03:41:46Z")
The ATM card that I had (note Mods I no longer have this account so there is no risk here) on my business account was not used much so I wrote the PIN on the card in an encryption.
I’ll add that it is a four digit number.
The number I wrote on the card is:
49236913293574598
I know that a PIN is not to be written on the card, but I did not really write the number on the card and do not believe that anybody could figure it out. Since the group here has more KSA’s than the average thug, I thought it would be interesting to put my code to the test.
There is a factual answer to this and I will post it after the TMs have had a crack at it.
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### Author:  [@Cabbage](https://boards.straightdope.com/u/Cabbage)
#### Post date: [September 11, 2003, 3:51am UTC](https://boards.straightdope.com/t/code-busters-guess-my-pin/200908/2 "2003-09-11T03:51:02Z")
What the hell:
0168?
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### Author:  [@Nobody\_s\_Fool](https://boards.straightdope.com/u/Nobody_s_Fool)
#### Post date: [September 11, 2003, 3:51am UTC](https://boards.straightdope.com/t/code-busters-guess-my-pin/200908/3 "2003-09-11T03:51:44Z")
2138
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### Author:  [@Taran](https://boards.straightdope.com/u/Taran)
#### Post date: [September 11, 2003, 3:59am UTC](https://boards.straightdope.com/t/code-busters-guess-my-pin/200908/4 "2003-09-11T03:59:32Z")
There is no solution that’s better than random guessing. The problem is, your algorithm is private, so giving us your number doesn’t really give us any information.
For example, let’s say that I tell you that I’ve encrypted my 4-digit PIN, and the result is 2222. This number could be the product of any number of algorithms:
PIN#+1
PIN#-1
PIN#\*2
(PIN#\*13 mod 11)^4
…well ok, not that last one. But do you see why we don’t have enough info to solve the problem?
All that said, if you put a gun to my head I’d choose 4627
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### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [September 11, 2003, 4:05am UTC](https://boards.straightdope.com/t/code-busters-guess-my-pin/200908/5 "2003-09-11T04:05:18Z")
4939
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### Author:  [@John\_Kentzel-Griffin](https://boards.straightdope.com/u/John_Kentzel-Griffin)
#### Post date: [September 11, 2003, 4:32am UTC](https://boards.straightdope.com/t/code-busters-guess-my-pin/200908/6 "2003-09-11T04:32:43Z")
Is it 0000? No?
0001? No?
0002? No?
How about 0003? No?
How many tries do I get? Am I close?
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### Author:  [@Peregrine](https://boards.straightdope.com/u/Peregrine)
#### Post date: [September 11, 2003, 4:35am UTC](https://boards.straightdope.com/t/code-busters-guess-my-pin/200908/7 "2003-09-11T04:35:31Z")
I’ll take 6178.
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### Author:  [@Joe\_Random](https://boards.straightdope.com/u/Joe_Random)
#### Post date: [September 11, 2003, 4:47am UTC](https://boards.straightdope.com/t/code-busters-guess-my-pin/200908/8 "2003-09-11T04:47:42Z")
My guesses are 2138 and 4625
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### Author:  [@Joe\_Random](https://boards.straightdope.com/u/Joe_Random)
#### Post date: [September 11, 2003, 4:48am UTC](https://boards.straightdope.com/t/code-busters-guess-my-pin/200908/9 "2003-09-11T04:48:56Z")
> [@](#):
>
> \*Originally posted by Joe Random \*
> \*\*My guesses are 2138 and 4625 \*\*
After posting, I see that **Nobody’s Fool** went with 2138, so I’ll go with 4625.
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### Author:  [@commasense](https://boards.straightdope.com/u/commasense)
#### Post date: [September 11, 2003, 4:54am UTC](https://boards.straightdope.com/t/code-busters-guess-my-pin/200908/10 "2003-09-11T04:54:39Z")
1234?
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### Author:  [@Deathstatic](https://boards.straightdope.com/u/Deathstatic)
#### Post date: [September 11, 2003, 5:13am UTC](https://boards.straightdope.com/t/code-busters-guess-my-pin/200908/11 "2003-09-11T05:13:17Z")
I see Nobody’s Fool’s reasoning that each number comes after each 9… so my guess opposite of his would be 4625.
Then again, that is boring… if you take each number and multiply it by the next number all of them beautifully go into 3 except for **5745** , which is all together.
I have come up with all sorts of crazy schemes on figuring this one out. SO in answer to your question… I have no idea and I hate you. I wish I never would have found this thread because I have actually fallen down stairs marvelling at Fibonacci numbers. It was an excellent number theory class…
maybe 2140? MAKE IT GO AWAY!! TELL ME THE ANSWER!
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### Author:  [@Askance](https://boards.straightdope.com/u/Askance)
#### Post date: [September 11, 2003, 5:17am UTC](https://boards.straightdope.com/t/code-busters-guess-my-pin/200908/12 "2003-09-11T05:17:51Z")
This is just a kudos for all posters so far for not saying “PIN number”. Thank you.
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### Author:  [@Deathstatic](https://boards.straightdope.com/u/Deathstatic)
#### Post date: [September 11, 2003, 5:21am UTC](https://boards.straightdope.com/t/code-busters-guess-my-pin/200908/13 "2003-09-11T05:21:57Z")
rather… are divisible by 3. 5745!!
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### Author:  [@Beryl\_Mooncalf\_1](https://boards.straightdope.com/u/Beryl_Mooncalf_1)
#### Post date: [September 11, 2003, 5:23am UTC](https://boards.straightdope.com/t/code-busters-guess-my-pin/200908/14 "2003-09-11T05:23:10Z")
6913
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### Author:  [@Deathstatic](https://boards.straightdope.com/u/Deathstatic)
#### Post date: [September 11, 2003, 5:32am UTC](https://boards.straightdope.com/t/code-busters-guess-my-pin/200908/15 "2003-09-11T05:32:57Z")
No, no… 1954
muahahahaahah… help me
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### Author:  [@Nanoda](https://boards.straightdope.com/u/Nanoda)
#### Post date: [September 11, 2003, 5:48am UTC](https://boards.straightdope.com/t/code-busters-guess-my-pin/200908/16 "2003-09-11T05:48:30Z")
Since your algorithm is not immediately obvious, finding a random set of numbers generated from a random set of other numbers is rather impossible.
OTOH, my friend and I had nothing better to do for 10 minutes, so:
After each 9: 2138
Before each 9: 4625
Using first 4 digits as index: 3292
Using first 4 digits as index into next 13: 3791
Use current digit as look-ahead value for next digit: 4634
And that’s all the time I’m wasting on this. 😉
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### Author:  [@hajario](https://boards.straightdope.com/u/hajario)
#### Post date: [September 11, 2003, 5:50am UTC](https://boards.straightdope.com/t/code-busters-guess-my-pin/200908/17 "2003-09-11T05:50:50Z")
6752, I think.
This really should go in IMHO because it is more of a puzzle and you know the answer.
Haj
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### Author:  [@trabi](https://boards.straightdope.com/u/trabi)
#### Post date: [September 11, 2003, 6:02am UTC](https://boards.straightdope.com/t/code-busters-guess-my-pin/200908/18 "2003-09-11T06:02:41Z")
6178 (The only numbers that aren’t repeated.)
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### Author:  [@Joe\_Random](https://boards.straightdope.com/u/Joe_Random)
#### Post date: [September 11, 2003, 6:02am UTC](https://boards.straightdope.com/t/code-busters-guess-my-pin/200908/19 "2003-09-11T06:02:52Z")
Here’s another guess (if multiple guesses are allowed). Since my last one was based on a simple algorithm, I decided to try something more complex.
The sequence **49236913293574598** is 17 digits long, and 17 is a prime number.
The number sequence can also be broken into four blocks, each of which _also_ contains a prime number of digits (representing the first four primes, by the way).
**49 236 91329 3574598**
Notice that there are four groups: One for each digit of the PIN. Anyone with a basic understanding of prime numbers could reach this point with with no need for fancy calculations. So my next part will be just as simple. I’m going to add the digits in each block, and keep adding until I get a single digit. So:
4 + 9 = 13
1 + 3 = **4**
2 + 3 + 6 = 11
1 + 1 = **2**
9 + 1 + 3 + 2 + 9 = 24
24 = **6**
3 + 5 + 7 + 4 + 5 + 9 + 8 = 41
4 + 1 = **5**
So you end up with a PIN of **4265**.
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### Author:  [@trabi](https://boards.straightdope.com/u/trabi)
#### Post date: [September 11, 2003, 6:07am UTC](https://boards.straightdope.com/t/code-busters-guess-my-pin/200908/20 "2003-09-11T06:07:26Z")
Oops, **Peregrine** already thought of that.
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