Ever since Douglas Adams’s Hitchhiker’s Guide to the Galaxy was first published, amateur mathematicians have sought to give explanations, with varying degrees of seriousness, as to why forty-two is The Answer to Life, the UniversePlanetmathPlanetmath, and Everything.

In the Adams book, 42 is the answer given by the computer Deep Thought, which then tells the people waiting to hear the answer that they don’t know what the question is. Arthur Dent tries to assemble the question from Scrabble tiles, coming up with the question ”What do you get if you multiply six by nine?” The answer is 54=4213. Adams says he did not intend to reference base 13 at all, and thus 54 would be a red herring in a search for the question.

From a purely mathematical point of view, the most interesting thing about 42 could be that it could be the third moment of the Riemann zeta functionDlmfDlmfMathworldPlanetmath, the leading coefficient of


expanded in powers of log(T).

The third primary pseudoperfect number and the productPlanetmathPlanetmath of the first three members of Sylvester’s sequenceMathworldPlanetmath, 42 is the second sphenic numberMathworldPlanetmath, but doesn’t seem to be the first of any interesting integer sequence (at least any sequence with the keywords ”core” or ”nice” in the OEIS). It does belong to several other interesting sequences, however, that of the Catalan numbersDlmfMathworldPlanetmath to name just one more.

When the 42nd Mersenne primeMathworldPlanetmath was discovered in 2005, Weisstein jokingly remarked that the answer ”is somehow contained in the 7.8 million decimal digits of that” prime. Berggren, Borwein and Borwein (authors of Pi: A Source Book) have also looked for 42 in the decimal expansions of π and 1π, finding ”042” at the fifty billionth position in both.


  • 1 J. P. Keating and N. C. Snaith, “Random Matrix Theory and θ(12+it)”, Commun. Math. Phys. 214, (2000): 57 - 89
  • 2 L. Berggren, J. Borwein, and P. Borwein, Pi: A Source Book, New York: Springer-Verlag (1997)
  • 3 E. Weisstein, “” Mathworld
Title forty-two
Canonical name Fortytwo
Date of creation 2013-03-22 16:28:37
Last modified on 2013-03-22 16:28:37
Owner CompositeFan (12809)
Last modified by CompositeFan (12809)
Numerical id 8
Author CompositeFan (12809)
Entry type Feature
Classification msc 11A99