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Is there a way to represent Knuth's up-arrow notation in Wolfram|Alpha?

Posted 9 years ago
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I am new to the community, but have run into a bit of a wall. I am trying to do various calculations that require the evaluation of reletively small (but still very large) numbers that are represented in Knuth's up-arrow notation. I have done some research and tried various things, but I unfortunately currently do not have Mathematica installed and have to solely rely on Wolfram|Alpha. I have found no way to represent the triple arrow notations, and smaller, other than breaking them up into series of parenthesized exponents. This is somewhat time consuming and brings in the possibility for error, which is unacceptable because the last 6 digits of each number are what I care about, so any error is catastrophic.

Example: $2??10 = ...948736$

Here are some links for the definition of Knuth's up-arrow notation, since I'm sure many of you don't know it since it's relatively obscure: WolframMathworld


Thank you ever so much, even if you only tell me it cannot be done,

James C.

POSTED BY: James Counterman

Wolfram|Alpha understands some Mathematica syntax, for example the last 6 digits of 2 ?? 10 can be computed by

Nest[Mod[2^#, 10^6] &, 1, 10]

W|A link, see also Power Tower at Mathworld.

POSTED BY: Ilian Gachevski
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