Sunday, January 20, 2008

What's the next term?

Here's one of those sequence questions that testers love so much:

What is the next term of this sequence?

0, 1, 2, 8.252 x 10^2466, ...

Here, "10^2466" means "ten to the 2466th power." The corresponding term is necessarily slightly approximate, since it contains 2467 decimal digits.

5 Comments:

At 9:46 PM , Anonymous Anonymous said...

Six?

 
At 3:16 PM , Blogger Wabulon said...

Er, that's not the answer the problem comes with...

 
At 3:22 PM , Anonymous Andy Stedman said...

Any chance that even the decimals shown for the huge number are wrong?

I have 0, 1, 2, 8.72598x10^2466, 1.02019x10^3910 ...

This is 1+n^8195, n=-1,0,1,2,3...

 
At 4:46 PM , Blogger Wabulon said...

Congratulations, Andy! You have in effect solved it--at least, you have found a valid solution.

Indexing from zero:

t(n) = 1 + (n-1)^p

where p = (2466+log 8.252)/log 2.

However, p is not an integer, which gives a problem with (-1)^p.

The best kludge I can come up with:

t(n) = 1 + (n-1) |(n-1)^(p-1)|.

This is required, because "8.252" is right. But your solution is in principle entirely valid. Again, congratulations. The next term is then 1 + 3^p. This is a big jump, but nothing compared with the previous jump, relatively speaking. In the limit, the ratio of successive terms is one. The order of growth is polynomial.

I like my answer better, because it is much simpler, and the jumps get hugely huger every time.

 
At 4:52 PM , Blogger Wabulon said...

In the above comment, p = 8223 approximately.

 

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