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February 15th, 2012, 09:06 AM   #1
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Can I give you guys a number theory related riddle?

This is the sequence, that contains 10 numbers.
Find the eleventh one and the pattern.

20-24-31-34-36-41-48-50-54-57-?

Yes, 20 is the first number.
Note: the answer is NOT trivial.
I can give a hint if you want to.
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February 15th, 2012, 06:44 PM   #2
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Re: Can I give you guys a number theory related riddle?

Here's my 'theory'

look at the differences between consecutive terms

4 7 3 2 5 7 2 4 3

each difference appears twice EXCEPT 5 so the next difference must be 5 making the next number of your sequence 57 + 5 = 62
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February 15th, 2012, 07:14 PM   #3
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Re: Can I give you guys a number theory related riddle?

I cheated and found the sequence on OEIS, and I don't feel bad for having cheated because I would never have figured it out on my own!
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February 15th, 2012, 07:15 PM   #4
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Re: Can I give you guys a number theory related riddle?

so what is the answer Mark?

oh, 69...
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February 15th, 2012, 07:28 PM   #5
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Re: Can I give you guys a number theory related riddle?

Yes, 69 is the next number in the sequence.
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February 15th, 2012, 11:50 PM   #6
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Re: Can I give you guys a number theory related riddle?

Please post the logic as well please .
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February 16th, 2012, 03:07 PM   #7
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Re: Can I give you guys a number theory related riddle?

You can find the logic in oeis.org website... "Numbers n such that 6*n-1 and 6*n+1 are twin composite odd numbers."

Anyway here i have my own sequence, find the next term:
1-1-1-31-381-2451-10921-38221-???????
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February 16th, 2012, 06:47 PM   #8
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Re: Can I give you guys a number theory related riddle?

[edit].....112561...[endedit]

but no help from oeis

i can explain if anyone asks...

here's a sequence i solved on another forum, not on file at oeis

1,2,3,4,5,8,7,16,9,...

find the next term and the general rule
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February 16th, 2012, 07:05 PM   #9
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Re: Can I give you guys a number theory related riddle?

The nth term is as follows:

For odd n:

For even n:

So, the next or 10th term is
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February 16th, 2012, 07:16 PM   #10
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Re: Can I give you guys a number theory related riddle?

very good, can you get the one given by THEBROKER...?
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