Can I calculate ((((a ^ n) ^ n) ^ ...) mod m) and (a ^ (n ^ (n ^ (...))) mod m) (b times n) effectively ?

Revision en3, by SPyofgame, 2020-06-28 03:23:38
In problem $$$\overbrace{(((a ^ n) ^ {{}^n}) ^ {{}^{{}^{...}}})}^{b\ times\ n} \mod m$$$

  • My approach is calculating each part $$$((a ^ n) \mod m)$$$ then $$$(((a ^ n) ^ n) \mod m) = ((t ^ n) \mod m)$$$ ... all together in $$$O(\log n)$$$ each part and $$$O(b \times \log n)$$$ total time complexity

  • Can I improve it somehow faster where $$$b$$$ is large ($$$b \leq 10^{16}$$$) and ($$$m$$$ can be composite number)

In problem $$$\overbrace{a ^ {(n ^ {(n ^ {(...)})})}}^{b\ times\ n} \mod m$$$

  • I only know the way to use bignum to calculate $$$n ^ n$$$ then $$$n ^ {n ^ n}$$$ all together then I just have to calculate the modulo of $$$a ^ {...} \mod m$$$ but the total complexity will be very huge (since the number of digits of bignum will raise very fast)

  • Can I apply these formula from phi-function:

$$$a ^ {\phi(m)} \equiv 1 \pmod m$$$
$$$a ^ n \equiv a ^ {n \mod \phi(m)} \pmod m$$$
$$$a ^ n \equiv a ^ {\phi(m) + (n \mod \phi(m))} \pmod m$$$
  • Can I improve it somehow faster where $$$n$$$ is large ($$$n \leq 10^{16}$$$) and ($$$m$$$ can be composite number)
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  Rev. Lang. By When Δ Comment
en3 English SPyofgame 2020-06-28 03:23:38 130 Tiny change: '(m)} \pmod m$$\n$$a ^ ' -> '(m)} \pmod(m)$$\n$$a ^ '
en2 English SPyofgame 2020-06-28 03:17:37 68
en1 English SPyofgame 2020-06-28 03:16:19 989 Initial revision (published)