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stackermann is a program that calculates the Ackermann function. It utilises GMP in conjunction with a simplistic stack data-type to calculate the enormous values efficiently.


  • UNIX-like system (probably includes Cygwin; not tested, though.)
  • ≥ gmp-4.0

Additionally, accurate computation timing requires librt; this is used by default and is present on just about any sane system.

Obtaining stackermann

stackermann is available as a source tarball at Direct link to the latest version.

Installation follows the usual configure/make/make install procedure.

Quick overview

Normal usage

Given m and n, stackermann simply calculates the value and prints it to stdout:

$ stackermann 4 1
A(4, 1)=65533

Use the -t option to suppress the leading A(m, n)=:

$ stackermann -t 4 1

If n is not given, n=m is assumed:

$ stackermann 3
A(3, 3)=61

The -s option may be used to additionally print computation statistics to stderr:

$ stackermann -s 3
A(3, 3)=61
Processing time: 0.001 s.
8 stack ops; max stack size 4 (~72 bytes).

Benchmark mode

In benchmark mode (the -b option), stackermann does not print the calculated value at all; instead, it prints statistics on what it took to calculate it. The output produced is printed as a space-separated list of—respectively—total computation time in seconds, total number of stack pushes, maximum number of stack entries, and approximate maximum stack size in bytes.

$ stackermann -b 4 2
0.050 131103 65534 1048552

Additional options

For an up-to-date overview of all available options and features, see the manpage included in the source tarball.

Limitations, bugs and feedback


To improve efficiency, stackermann does not allow the m-parameter to be greater than 255. In reality, this is unlikely to pose a problem, since no current computer will have the memory or speed required to compute the values with high m-parameters anyway. This is not a bug; do NOT report it as one!

Bugs and feedback

Report bugs through MantisBT at (you will need to sign up for an account). If and only if you're unable to use MantisBT, you can report bugs via email at bugs[at]proj[dot]penguindevelopment[dot]org.

Send your feedback to feedback[at]proj[dot]penguindevelopment[dot]org.

Before reporting a bug, make sure it isn't listed on MantisBT!