A few parts appearing in this excursions to primes:

- We formulate
**Goldbach** conjectures or questions
in division algebras and Eisenstein integers.
Gauss |
Quaternion |
Eisenstein |

Every **even** Gaussian integer a+ib with a,b larger than 1
is the sum of two Gaussian primes with positive coefficients. |
Every Lipschitz quaternion with entries larger than 1
is the sum of two Hurwitz quaternions with positive coefficients. |
Every Eisenstein integer a+b w with a,b larger than 3
is the sum of two Eisenstein primes with positive coefficients. |

3+6i=(1+i)+(2+5i) |
(4+2i+j+2k)=(3+i+j+k)/2+(5+3i+j+3k)/2 | 5+2w = (2+w) + (3+w) |

In the Gaussian and Quaternion case, we can relate to Landau
or Bunyakowsky type conjectures. In the Octonion case, the statement is
false for Klainian primes but looks reasonable for Kirmse primes.
In the Quaternion and Eisenstein case, **no evenness is necessary**.

- We look at the zeta function in each of the division algebras and relate to
the usual zeta function. We show pictures of the roots of the zeta function for
Gaussian integers.
- We illustrate the Gaussian, Hurwitz and Kirmse primes with pictures.
- We look at almost periodic matrices which are the real part of van der
Monde matrices. We can estimate the determinant in special Diophantine cases
but admire mostly the beautiful snow flake spectra. We have looked at these spectra
already in 2008 and used it in computer algebra projects in 2010.
- Gaussian integers define a graph, where two positive integers a,b are
connected, if a+ib is prime. The growth rate of the Euler characteristic of this
graph is related to the growth of primes.
- We look at greatest common divisor matrices for which the determinants
are explicitly known. The spectra in the complex have a spiral shape feature.
These matrices were used heavily in our
2015 linear algebra course.
- We look at matrices defined by Gaussian integers. We observe that they become
invertible if large enough and some symmetry is avoided. We investigate the growth
of the determinant, trace, coefficients of the characteristic polynomials.
While writing the exam
for Math 21b in the spring 2016, Gaussian matrices were used as an inspiration.

This project was done from April 27 (writing the 21b exam), 2016 to June 19, 2016
(start of summer school).