Re:Mysterious number 6174
by jacquesm on Friday February 13, 2009 @08:18PM
(#480727)
A nice example is the divisibility of numbers, by rearranging the digits and performing simple operations on them you can quickly figure out if a number is divisible by a certain other number without actually doing the division.
"a number is divisible by 11 if and only if when you add the digits that are an odd number of places from the right, and then you add the digits which are an even number of places from the right, the difference of these is divisible by 11."
for an example see:
http://en.wikipedia.org/wiki/International_Bank_Account_Numb...
or google for 'eleven check'.
A snippet from a yahoo answers page:
"a number is divisible by 11 if and only if when you add the digits that are an odd number of places from the right, and then you add the digits which are an even number of places from the right, the difference of these is divisible by 11."