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extract from list and keep track

• To: mathgroup at smc.vnet.net
• Subject: [mg62131] extract from list and keep track
• From: Andrea <andrea at radargift.com>
• Date: Sat, 12 Nov 2005 03:31:47 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

I'm trying to write a program for the following. Seems simple, but I'm 
unable to to do it:

I have a list of increasing odd numbers. I want to create a table that 
indicates which numbers in this list are 1(mod 8) and 7(mod 8) and what 
position in the list these numbers have.
Then I would like to have them removed form the list to get a new (reduced) 
list.


Example: 3, 7, 9, 21, 43, 57, 63, 71, 75, 99.   I want to form this a Table:

2      7
3      9
6    57
7    63
8    71

7 is 7(mod 8) and is the 2nd member in the list, 9 is 1(mod 8) and is the 
3rd member in the list, etc.

The next list would become, having removed the ones in the table:

3, 21, 43, 75, 99

And I would be using some other congruence criteria. Etc.

Thanks,
Andrea

• Follow-Ups:
  • Re: extract from list and keep track
    • From: <bsyehuda@gmail.com>
  • Re: extract from list and keep track
    • From: danl@wolfram.com