Math sites & tools

(1) Interactive Mathematics

http://www.intmath.com/

(2) Number Base Calculator

http://www.cleavebooks.co.uk/scol/calnumba.htm

(3) Arithmetic Game

http://arithmetic.zetamac.com/

(4) Number Dictionary

http://www.numdic.com/

(5) Rethinking Pythagoras

http://mathdl.maa.org/mathDL/23/?pa=content&sa=viewDocument&nodeId=3568