O'Neil, Catherine  
   M.I.T. Number theory, Arithmetic algebraic geometry.
   http://www-math.mit.edu/~coneil/

Omar, Sami  
   University of Essen. Zeroes of L-functions and related topics; Cryptography; Computational number theory; Random Matrix theory and L-functions.
   http://www.exp-math.uni-essen.de/~omar/

Ono, Ken  
   University of Wisconsin. Combinatorics and Number Theory involving Elliptic curves, L-functions, modular forms and partitions. Publications, activities, resources.
   http://www.math.wisc.edu/~ono/

Ono, Takashi  
   Johns Hopkins University. Contact information.
   http://www.math.jhu.edu/faculty/Ono.html

Oort, Frans  
   University of Utrecht. Algebraic geometry and number theory. Publications, links.
   http://www.math.ruu.nl/people/oort/

Ohno, Yasuo  
   Kinki University. Siegel modular forms and Jacobi forms; Zeta functions associated with prehomogeneous vector spaces; Poly-Bernoulli numbers; Invariant theory. Papers, theses.
   http://www.math.kindai.ac.jp/math/ohno/ohnore.html

Okazaki, Ryotaro  
   Doshisha University. Unit Equation; Class Field Theory of CM-fields; Continued Fractions. Papers, teaching materials.
   http://www1.doshisha.ac.jp/~rokazaki/

Osburn, Robert  
   McMaster University. Modular forms, combinatorics, partition function. Publications.
   http://www.math.mcmaster.ca/~osburnr/

Ouyang, Yi  
   University of Toronto. Algebraic number theory and arithmetic geometry: cohomological tools to study the arithmetic properties of number fields. Publications.
   http://www.math.toronto.edu/youyang/

Ochiai, Tadashi  
   Osaka University. Number theory, arithmetic geometry. Papers, preprints.
   http://www.math.wani.osaka-u.ac.jp/group/ochiai/index-e.html

Oyono, Roger  
   Universität Duisburg-Essen. Arithmetic on Jacobians. Publications, thesis.
   http://www.exp-math.uni-essen.de/~oyono/

Oman, Karl  
   Thiel College. Elementary and Algebraic Number Theory: Powerful Numbers, the abc Conjecture, and Ramanujan-Nagell Equations. Teaching information, Problem of the Week.
   http://www.thiel.edu/academics/math/Faculty/KOman/

Odgers, Ben  
   University of Bristol. Prime numbers, the Riemann zeta function, L-functions, and random matrix theory.
   http://www.maths.bris.ac.uk/~mabeo/