Question 1210183
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The correct answer is 78960.  How do I know?  I wrote a program in LibertyBasic.
I let A and B represent one pair of siblings, C and D represent another pair of
siblings, and D and E represent another set of siblings. I let the X's refer to
the 4 empty chairs.

My program ensures that A and B are never next to each other, that C and D are
never next to each other, and that E and F are never next to each other. 

The program I wrote also produces no duplications. For every new seating
arrangement my program finds, my program always makes sure that it is NEVER
identical to any one of the other arrangements it has found so far.  So all
78960 arrangements my program found are definitely unique.

Except for the 4 X's for the empty chairs, the output shows all possible
arrangements in alphabetical order.

Here are the first 10 of my output.

1             ACBDEXFXXX
2             ACBDEXXFXX
3             ACBDEXXXFX
4             ACBDEXXXXF
5             ACBDFXEXXX
6             ACBDFXXEXX
7             ACBDFXXXEX
8             ACBDFXXXXE
9             ACBDXEXFXX
10            ACBDXEXXFX

Here are 10 where they changed from beginning with A to beginning with B.

8276          AXXXXFCEDB
8277          AXXXXFDBCE
8278          AXXXXFDBEC
8279          AXXXXFDEBC
8280          AXXXXFDECB
8281          BCADEXFXXX
8282          BCADEXXFXX
8283          BCADEXXXFX
8284          BCADEXXXXF
8285          BCADFXEXXX

Here are 5 where they changed from beginning with DE to DF.

28169         DEXXXXFACB
28170         DEXXXXFBCA
28171         DFACBEXXXX
28172         DFACBXEXXX
28173         DFACBXXEXX

Here are 5 where they changed from beginning with XE to XF.


66679         XEXXXFDACB
66680         XEXXXFDBCA
66681         XFACBDEXXX
66682         XFACBDXEXX
66683         XFACBDXXEX

Now I'll skip on down to the final 10.

78951         XXXXFDACBE
78952         XXXXFDACEB
78953         XXXXFDAEBC
78954         XXXXFDAECB
78955         XXXXFDBCAE
78956         XXXXFDBCEA
78957         XXXXFDBEAC
78958         XXXXFDBECA
78959         XXXXFDEACB
78960         XXXXFDEBCA

I can't post the entire output here, as it's too long. But you can see how the
X's moved gradually from right to left.
  
78960 is the correct answer, with 3 pairs of siblings, and 4 empty chairs.

Edwin</pre>