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10 votes
1 answer
2k views

How can I effectively compute tetration $\pmod a$?

Is there some general technique to compute tetration and pentation mod some number? $m \uparrow^2 n \pmod a$ and $m \uparrow^3 n \pmod a$ I know about Euler's theorem to compute $m \uparrow n \pmod a$...
Tim Marinin's user avatar
3 votes
1 answer
437 views

$\lim_{b \rightarrow \infty} {^{b}a} \in \mathbb{Q}_p$ for any $a \in \mathbb{Z}^+$?

$\newcommand\tetra[2]{{^{#1}{#2}}}$In a recent discussion on the Tetration Forum (see https://math.eretrandre.org/tetrationforum/showthread.php?tid=1703&page=2), it has been pointed out how my ...
Marco Ripà's user avatar
  • 1,451
2 votes
1 answer
513 views

Prove ${^{b}a} \equiv {^{b+1}} a \pmod {10^{\lfloor{\log_{10} (^{b}a) }\rfloor + 1}} \Rightarrow a=5$ as $a$ and $b$ are two integers greater than $1$

$\DeclareMathOperator\len{len}$Let $a, b \in \mathbb{N} -\{ 0, 1 \}$ and define ${^{b}a}$ to be $a^a$ if $b = 2$ and $a^{\left(^{b-1}a \right)}$ if $b \geq 3$ (e.g., ${^{3}5} = 5^{\left( 5^5 \right)} =...
Marco Ripà's user avatar
  • 1,451
1 vote
0 answers
152 views

A new Conjecture at OEIS sequence A376842

Here is a new conjecture of mine from the appendix of an unpublished manuscript currently under review. Let $b \in \mathbb{Z}^+$ and assume that $n$ is an integer greater than $1$ and not a multiple ...
Marco Ripà's user avatar
  • 1,451
0 votes
0 answers
58 views

Showing that the congruence speed of any integer exponentiation $a^b$ is constant and $\geq 1$ iff $a>1$ is a multiple of $10$

Years ago, I defined the "congruence speed" (radix-$10$) of the integer tetration $^{b}a$ as $V(a,b)$, which is the number of the new(!) rightmost digits that freeze when we move from $b \in ...
Marco Ripà's user avatar
  • 1,451
0 votes
0 answers
129 views

Defining the number of rightmost frozen digits of Graham's number

It is well-known that (in radix-$10$) Graham's number, $G$, can be expressed as a tetration with base $3$ and a very large hyperexponent $\tilde{b}$. Thus, we can write that $\exists! \hspace{1mm} \...
Marco Ripà's user avatar
  • 1,451