# discrete math- sequence question

Discussion in 'Homework Help' started by s3b4k, Mar 8, 2010.

1. ### s3b4k Thread Starter Member

Feb 15, 2010
38
0
I need to come up with a rule or a formula for the following:

1,2,2,2,3,3,3,3,3,5,5,5,5,5,5,5.....

Jul 7, 2009
1,585
141
Hint: 2*n + 1 and primes

3. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,699
909
There may be more than one pattern that gives that initial sequence. One solution is: the digits 1,2,3,and 5 are primes (positive). The repeat frequencies seem to follow just the odd numbers. The next three repeat frequencies would be 9, 11 and 13. That is, the next two sequences would be nine 7's, then eleven 11's.

John

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4. ### s3b4k Thread Starter Member

Feb 15, 2010
38
0
ok thanks a lot for the help, but is there an exact formula i can use, or is it only solvable by explaining it?

5. ### Markd77 Senior Member

Sep 7, 2009
2,803
594
1 isn't normally considered a prime if that makes any difference.

Jan 18, 2008
5,699
909
7. ### Markd77 Senior Member

Sep 7, 2009
2,803
594
I searched for the sequence on google and found this. Still no idea what it is.

8. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,699
909
For (b) the sequence starts with 1, and if there are at least 2 previous term, then the subsequent term is the sum of the previous two terms, otherwise it is 2 (or alternatively, the previous term is doubled). The replicates of each term is as in the first problem.

I am too tired to look at (a) now. Perhaps this question should have its own thread.

John

Edit: For (a) here's a reference: http://mathworld.wolfram.com/Near-SquarePrime.html

Last edited: Mar 11, 2010
9. ### s3b4k Thread Starter Member

Feb 15, 2010
38
0
this question is driving me nuts, are the next three terms going to be 8,8,8 or 7,7,7. because it good either be prime numbers or just the sum of the previous numbers, but if its the sum of the previous numbers how do you get the two there

10. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,699
909
There is not enough information to know for sure. The sum of the previous numbers (Fibonacci, 8) may be what your teacher wants. In either case, you have to make an explanation for the first number (or absence thereof).

John

PS, when I went to school 1 was still prime. But then, it was a public school.

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