Lucky numbers

BRINCKOVÁ, Jaroslava - DZÚRIKOVÁ, Iveta - KLENOVČAN, Pavel. Lucky numbers. In Lower secondary school teacher training in mathematics : comparison and best practices. - Pisa : Edizioni Plus - Pisa University Press, 2006. ISBN 978-88-8492-436-0, s. 81-84. Dostupné na internete: <http://losstt-in-math.dm.unipi.it/>