-
http://www.math.unideb.hu/
Mathematical Institute, University of Debrecen -
http://www.math.leidenuniv.nl/
Mathematical Institute, Leiden University -
http://escherdroste.math.leidenuniv.nl/
Applying mathematics to Escher's Print Gallery -
http://www2.warwick.ac.uk/fac/sci/maths/research/interests/number_theory
Warwick Number Theory Group -
http://www.numbertheory.org/
Number Theory Web -
http://front.math.ucdavis.edu/
Front for the Mathematics Arxiv -
http://listserv.nodak.edu/archives/nmbrthry.html
Number Theory List