Mathematics for Computer Science

“mcs” — 2017/3/3 — 11:21 — page 322 — #330
322
Chapter 9
Number Theory
The Riemann Hypothesis
The formula for the sum of an infinite geometric series says:
1 C x C x 2 C x 3 C D 1
1 x :
Substituting x D 1 2 s , x D 1 3 s , x D 1 5 s , and so on for each prime number gives a
sequence of equations:
1 C 1 2 s C 1
2 2s C 1
2 3s C D 1
1 1=2 s
1 C 1 3 s C 1
3 2s C 1
3 3s C D 1
1 1=3 s
1 C 1 5 s C 1
5 2s C 1
5 3s C D 1
1 1=5 s
Multiplying together all the left-hand sides and all the right-hand sides gives:
1X
nD1
1
n s D
Y
p2primes
:
1
1 1=p s :
The sum on the left is obtained by multiplying out all the infinite series and applying
the Fundamental Theorem of Arithmetic. For example, the term 1=300 s
in the sum is obtained by multiplying 1=2 2s from the first equation by 1=3 s in
the second and 1=5 2s in the third. Riemann noted that every prime appears in the
expression on the right. So he proposed to learn about the primes by studying
the equivalent, but simpler expression on the left. In particular, he regarded s as
a complex number and the left side as a function .s/. Riemann found that the
distribution of primes is related to values of s for which .s/ D 0, which led to
his famous conjecture:
Definition 9.9.6. The Riemann Hypothesis: Every nontrivial zero of the zeta
function .s/ lies on the line s D 1=2 C ci in the complex plane.
A proof would immediately imply, among other things, a strong form of the Prime
Number Theorem.
Researchers continue to work intensely to settle this conjecture, as they have for
over a century. It is another of the Millennium Problems whose solver will earn
$1,000,000 from the Clay Institute.