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Euler's Constant was first introduced by Leonhard Euler (1707-1783)
in 1734 as the limit
It is also known as the Euler-Mascheroni constant (according to
Glaisher , the symbol g is probably due to the
geometer Lorenzo Mascheroni (1750-1800) who used it in 1790 while Euler used
the letter C).
g is deeply related to the Gamma function G(x) thanks to the
n > 0
and from this formula follows the relation
Gў(1) = -g.
We don't know if g is an irrational or a transcendental number. The question of it's irrationality (or not ?) has
challenged mathematicians since Euler, it remains a famous unresolved
problem. By computing sufficiently digits of g it has been shown
that if g is rational ( = p/q) then the denominator q must have at
least 242080 digits.
Even if g is less famous than the constants p and e, it
deserves a great attention since it plays an important role in Analysis (Gamma function, Bessel functions, exponential-integral, ...) and
occurs frequently in Number Theory (order of magnitude of
arithmetical functions for instance ).
Direct use of formula (1) to compute Euler constant is of
poor interest since the convergence is very slow. In fact, using the
harmonic number notation
Hn = 1+
we have the estimation
This estimation is the first term of an asymptotic expansion which can be
used to compute effectively g, as shown in next section.
Nevertheless, other formulae for g (see next sections) provide a
simpler and more efficient way to compute it at a large accuracy. The
estimation can be refined as :
During the year 1790, in ''Adnotationes ad calculum integrale Euleri'', Mascheroni made a similar calculation up to 32 decimal places. But, a
few years later, in 1809, Johann von Soldner (1766-1833) found a value of
the constant which was in agreement only with the first 19 decimal places of
Mascheroni's calculation ... Embarrassing !
It was in 1812, supervised by the famous Mathematician Gauss, that a young
calculating prodigy Nicolai (1793-1846) evaluated g up to 40 correct
decimal places, in agreement with Soldner's value .
In order to avoid such miscalculations (see also William Shanks famous error
on his determination of the value of p), digits hunters are using
different calculations to verify the result.
In 1887, Stieltjes computed z(2),z(3),...,z(70) to 32 decimal places
and extended a previous calculation done by Legendre up to z(35) with
16 digits. He was then able to compute Euler's constant to 32 decimal places
thanks to the fast converging sequence
g = 1-log(
k = 1
for large values of k
This relation is issued from properties of the Gamma function and a proof is
given in the Gamma function essay.
The bound RN = O(e-N) gives another method to compute g :
n = 1
-log(N)+O(e-N), a @ 3.59 (A2)
The constant a is such that NaN/(aN)! is of order e-N. To obtain d decimal places of g with (A2), the
formula should be used with N @ dlog(10) and computations should be
done with a precision of 2d decimal places to compensate for cancellation
in the sum for IN. This method was used by Sweeney to compute 3566
decimal places of g .
A refinement is obtained by approximating RN by its asymptotic
expansion, leading to the formula
n = 1
n = 0
+O(e-2N), b @ 4.32. (A3)
This improvement, also due to Sweeney , permits to take N @ d/2log(10) and to work with a precision of 3d/2 decimal places
to obtain d decimal places of g.
Notice that RN can be approximated as accurately as desired by using
Euler's continued fraction
eNRN = 1/n+1/1+1/n+2/1+2/n+3/1+3/n+ј
This can be used to improve the efficiency of the technique, but leads to a
much more complicated algorithm.
More information about this technique can be found in .
A better method (see also ) is based on the modified Bessel
functions and leads to the formula
- log(N) + O(e-4N),
n = 0
Hn, BN =
n = 0
where b = 4.970625759ј satisfies b(log(b)-1) = 3.
This technique is quite easy, fast and it has a great advantage compared to
Exponential integral techniques : to obtain d decimal places of g,
the intermediate computations can be done with d decimal places.
A refinement can be obtained from an asymptotic series of the error term. It
consists in computing
This is the first gamma computation
based on a binary splitting approach. He used a Sun SPARC Ultra, and the
computation took 160 hours. He also proved that if g is rational,
its denominator has at least 242080 decimal digits.
Sweeney's method (with N = 223 )
with binary splitting was used. The computation took 47 hours on a SGI
R10000 (256 Mo). The verification was done with the value N = 223+1.
X. Gourdon and P. Demichel
3) was used with a binary splitting process. The program
was from X. Gourdon and Launched by P. Demichel on a HP J5000, 2 processors
PA 8500 (440 Mhz) with 2 Go of memory.