Edition Associa¸c˜ao Ludus, Museu Nacional de Hist´oria Natural e da Ciˆencia, Rua da Escola Polit´ecnica 56 1250-102 Lisboa, Portugal email:
[email protected] URL: http://rmm.ludus-opuscula.org Managing Editor Carlos Pereira dos Santos,
[email protected] Center for Linear Structures and Combinatorics, University of Lisbon Editorial Board Aviezri S. Fraenkel,
[email protected], Weizmann Institute Carlos Pereira dos Santos Colin Wright,
[email protected], Liverpool Mathematical Society David Singmaster,
[email protected], London South Bank University David Wolfe,
[email protected], Gustavus Adolphus College Edward Pegg,
[email protected], Wolfram Research Jo˜ao Pedro Neto,
[email protected], University of Lisbon Jorge Nuno Silva,
[email protected], University of Lisbon Keith Devlin,
[email protected], Stanford University Richard Nowakowski,
[email protected], Dalhousie University Robin Wilson,
[email protected], Open University Thane Plambeck,
[email protected], Counterwave, inc Informations The Recreational Mathematics Magazine is electronic and semiannual. The issues are published in the exact moments of the equinox. The magazine has the following sections (not mandatory in all issues): Articles Games and Puzzles Problems MathMagic Mathematics and Arts Math and Fun with Algorithms Reviews News ISSN 2182-1976 Contents Page Math and Fun with Algorithms: Xiang-Sheng Wang Calculating the day of the week: null-days algorithm . 5 Games and Puzzles: David Singmaster Some early topological puzzles – Part 1 ............ 9 Mathematics and Arts: Pedro Freitas Almada Negreiros and the regular nonagon .......... 39 Mathematics and Arts: Ricardo Cunha Teixeira Patterns, mathematics and culture: The search for symme- try in Azorean sidewalks and traditional crafts ......