Introductory texts to mathematics I am interested in texts recomendations for a 14 years old boy who wants to study more mathematics than he does at school. He seems quite talented, but his knowledge of maths is rather low. I would prefer texts written by well known mathematicians. My first recommendation to him was Courant's book "What is mathematics?" for an introduction while I look for more systematic study texts. I am specially interested in an introductory study of calculus and elementary geometry (for introductions to number theory I think A. Baker or Hardy's books will fit). English, French or Spanish are ok.
Edit. Please note that I'm not interested in problem-solving books, nor lists of problems. Thank you anyway for those answers (Arnold's list seems interesting, even though for other purposes).
 A: I would recommend Mathematical Omnibus: Thirty Lectures on Classic Mathematics, by D. B. Fuks and Serge Tabachnikov: http://books.google.ru/books?id=bomkJMq2H9sC&source=gbs_similarbooks and also books from the series Kvant Selecta: http://books.google.ru/books/about/Kvant_Selecta.html?id=aJLcCFyLwhEC&redir_esc=y
P.S. For systematic study of elementary geometry a good book is Kiselev's Geometry (in two parts): http://www.amazon.com/Kiselevs-Geometry-Book-I-Planimetry/dp/0977985202
combined with Prasolov's "Problems in Plane and Solid Geometry": http://students.imsa.edu/~tliu/Math/planegeo.pdf
For an introductory study of  basics calculus, I recommend Spivak's "The Hitchhiker's Guide to Calculus": http://www.amazon.com/dp/0883858126/?tag=stackoverfl08-20
and then "Analysis by Its History", by Ernst Hairer and Gerhard Wanner: http://www.springer.com/gp/book/9780387945514
A: I support very much the idea to recommend the Fuks and Tabachnikov book as in the answer above, and in addition to this two book by Vladimir Arnold:


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*Arnold's problems book for school students, which is freely available via http://imaginary.org/sites/default/files/taskbook_arnold_en_0.pdf . Note that it is also available in many languages on the same web site.

*Arnold's Catastrophy Theory, which gives a great introduction to dynamical systems and related topics.
A: *

*Courant and Robbins, What is mathematics?

*Hilbert, Cohn-Vossen, Geometry and imagination.
