Monday, April 11, 2011

Just for gigs...

This is a sequel to my earlier post - Numbers: Not everything is magic.

If I show the numbers 1024, 2048, 4096... to a software geek, the immediate answer would be around bits and bytes. But these numbers have another peculiar pattern.
1024 is the first positive integer to satisfy the condition.
an+2 + an = (2a)n

It is followed by the remaining numbers. Check the following:
102422 + 102420 = 204820
204824 + 204822 = 409622
409626 + 409624 = 819224
819228 + 819226 = 1638426
1638430 + 1638428 = 3276828
……

Now the hack to find it.
an+2 + an = (2a)n
=>an (a2 + 1) = 2 n an
=>a2 + 1 = 2 n
=>a= (2 n - 1)1/2

Now, let us find out a way to solve the below equation:
an+x + an = (2a)n
=>an (ax + 1) = 2 n an
=>ax + 1 = 2 n
=>a= (2 n - 1)1/x

So, for n and n+4, the first positive integer to satisfy is 64.

Last but not the least for the post.
an+x + an = (k*a)n
=>an (ax + 1) = k n an
=>ax + 1 = k n
=>a= (k n - 1)1/x
So for k=3 and x = 1, the numbers are 2, 8, 26, 80...

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