[seqfan] need help with query

N. J. A. Sloane njas at research.att.com
Thu May 14 16:38:16 CEST 2009

Dear Seqfans,  Can people help with either of the following 
messages, which arrived in the past 24 hours?

Message 1:

Date: Wed, 13 May 2009 06:18:27 -0700 (PDT)
From: Kathy Suchanek <ksuchanek at yahoo.com>
Subject: what is the number for ?

This should be in a chart like tic tac toe.
7    4    8
3    9    7
6    5    10
?    8    4

Message 2:

Date: Thu, 14 May 2009 18:09:51 +0530
Subject: [seqfan] Request for seqid :A000217
From: nishant doshi <doshinikki2004 at gmail.com>

Respected sir,
  I have found that for the following problem we have the same sequence. the
problem is as follow.
  Assume that n persons are going in a road. there is a wall in between
 initially all are going in the direction of the wall on a road. here we
have to count the number of collisions between wall and person,AND between
two persons.
 They have to follow the condition that when a person is collision with wall
or other person than it has to change the direction. in the case if
collision between two persons, they both will reverse their direction. so
after fixed number of collision all the n persons are going in the direction
reverse to the wall. so te goal is to find the such number of collisions for
n persons.

the answer is #of_collision(n)=#of_collision(n-1)+n.

May I request to look for this problem.


Neil Sloane

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