This is what most of the Sri Lankans searching the solution in internet these days. (Actually the ones who attend the INFOTEL 2008 @ BMICH).
Here is the answer.
If you factor 123456 into its prime factors you get:
2 * 2 * 2 * 2 * 2 * 2 * 3 * 643 = 123456
That tells you that DEF=643. And ABC = 2 * 2 * 2 * 2 * 2 * 2 * 3 = 192
Answer:
192 * 643 = 123456
A=1
B=9
C=2
D=6
E=4
F=3
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