To be more exact and accurate, all puzzles (including sudoku), interactive mathematical games and even board games can help in the teaching and learning of mathematics.
It is obvious that NRICH knows that puzzles and interactive mathematical games allow students to learn and play at the same time.
My sudoku creation for the October 2008 edition of NRICH in nrich.maths.org :: Mathematics Enrichment :: Addition Equation Sudoku is the Addition Equation Sudoku.
It illustrates the concepts of addition and equations.
Beginning this month (November 2008), NRICH uses innovative flash interactivity for my sudoku creation ("LCM Sudoku") in nrich.maths.org :: Mathematics Enrichment :: LCM Sudoku II
The variant illustrates the concept of Least Common Multiples.
My first version of "LCM Sudoku", using numbers and unknown variables, was posted on nrich.maths.org :: Mathematics Enrichment :: LCM Sudoku
To be more specific, that variant should be called "Algebraic LCM Sudoku".
I have posted a more challenging version of "LCM Sudoku", which uses advanced sudoku techniques, this month (November 2008) on the site chinasudoku.com
For students who like fairy tales, they can try to solve another of my sudoku puzzle called "Story Sudoku".