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I want to write a math equation that needs power of dots. I tried these code

{2^{2^{2^{\ddots^{2}}}}}

But the dots needs to be rotated

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@user5376: you could perhaps use egreg's answer to a question about a rotated integral sign tex.stackexchange.com/questions/17416/… –  jfbu May 7 '11 at 11:01
    
@user5376: oh, sorry, I thought your dots were already with about the correct angle, as with \iddots from mathdots. Could prove easier indeed to rotate slightly \iddots than a lot \ddots, and perhaps actually \iddots already quasi solves your problem. –  jfbu May 7 '11 at 11:28
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3 Answers 3

Adapted from The TeXbook, Exercise 18.45:

\def\rddots#1{\cdot^{\cdot^{\cdot^{#1}}}}
$ 2^{2^{\rddots2}} $
\bye

enter image description here

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(+1) Again, I feel like it provides a better alignment than \iddots! –  chl May 7 '11 at 18:46
    
When used like this, on math.stackexchange.com each subsequent dot is smaller... –  Tomáš Zato Jan 26 at 0:40
    
@Tomáš: That's because MSE uses [mathjax], which is a bit different thing from TeX and I am not very familiar with it. There is a glyph with [unicode-math], \adots for U+022F0, but I don't think it's available with mathjax (nor if it's the appropriate glyph for this). If mathjax understands different math styles, you could try the more explicit definition: \def\rddots#1{{\scriptstyle\cdot}^{{\scriptstyle\cdot}^{{\scriptstyle\cdot}^{#1‌​}}}} –  morbusg Jan 26 at 9:06
    
@TomášZato: Or, with Unicode, something like: \def\sadots{{\scriptstyle\char"22F0\relax}} (note that there is no family or class definitions, so for use just in this context). –  morbusg Jan 26 at 9:12
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An easy way would be to replace \ddots by \udots from the MnSymbol package, or \iddots from mathdots (better rendering in math mode).

enter image description here

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I could not define the MnSymbol package, when I define it the program does not compile the file –  user5376 May 7 '11 at 8:09
    
@user5376 Add \usepackage{MnSymbol} in your preamble. Still, I'd recommend using \iddots instead. –  chl May 7 '11 at 8:11
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you could try (with 5 dots for the fun of it!):

\[
  {2^{2^{2^{\mathstrut^{.^{.^{.^{.^{.^{\raisebox{-.5\height}{$\scriptscriptstyle
                        2$}}}}}}}}}}}
\]

\[
  {2^{2^{2^{\mathstrut^{.^{.^{.^{.^{.^{\raisebox{-.25\height}{$\scriptscriptstyle
                        2$}}}}}}}}}}}
\]

or the simpler

\[
  {2^{2^{2^{\mathstrut^{.^{.^{.^{\raisebox{-.25\height}{$\scriptscriptstyle
                        2$}}}}}}}}}
\]

\[ 
  {2^{2^{2^{\mathstrut^{.^{.^{.^{2}}}}}}}}
\]

they give (respectively):

iterated powers of two

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@jbfu (+1) Your 2nd solution seems to provide a better alignment. –  chl May 7 '11 at 12:30
    
@chl yes, I agree. The \mathstrut is to put the first dot higher than where it would fall otherwise. One could fine-tune that positioning if needed. –  jfbu May 7 '11 at 12:55
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