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The Magic Cafe Forum Index » » Magical equations » » Powers of 2 *Si* (0 Likes) Printer Friendly Version

Scott Cram
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Playing around with the base 10 logarithms of powers of 2, I noticed an amusing pattern.

Here are the base 10 logarithms of the first 20 powers of 2. Notice the first digit to the right of the decimal point of each logarithm. They go in a very familiar pattern: 3, 6, 9, 2, 5, 8, 1, 4, 7, 0, then it repeats.

Does that pattern seem familiar to anyone or everyone? Smile
vindar
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Hi,

Indeed, this is fun Smile

The explanation is that log(10)/log(2) = 0.301... is close to 0.3. In this case, the sequence will fail after n=100.

If you take the first digit after the decimal point of the (simpler) sequence n*0.3 then the pattern will repeat infinitely: http://www.wolframalpha.com/input/?i=Tab......2C+100}].
Michael Daniels
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The last digit of successive multiples of 3 immediately springs to mind.

Mike
Scott Cram
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Quote:
On Apr 6, 2014, vindar wrote:
Hi,

Indeed, this is fun Smile

The explanation is that log(10)/log(2) = 0.301... is close to 0.3. In this case, the sequence will fail after n=100.

If you take the first digit after the decimal point of the (simpler) sequence n*0.3 then the pattern will repeat infinitely: http://www.wolframalpha.com/input/?i=Table[n*0.3%2C+{n%2C+1%2C+100}].


I'm familiar with why it works, but I just found it amusing, as I never thought about it that way before.

Quote:
On Apr 6, 2014, Michael Daniels wrote:
The last digit of successive multiples of 3 immediately springs to mind.

Mike


Michael, you're a true mathematician! Smile
Michael Daniels
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Too kind, Scott!

It's also interesting that this repeating sequence is the exact reverse of that obtained when considering the last digit of successive multiples of 7.

7,4,1,8,5,2,9,6,3,0, ...

Mike
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