Problems & Puzzles: Coll.20th

This collection of anniversary puzzles is dedicated
 to my friend Jaime Ayala, for his enthusiastic
 and challenging conversations 20 years ago,
those that are behind the launching of this site.


Coll.20th-xxx Puzzle's name Author(s)/Solvers Published Date
001 A Puzzle-sequence G. L. Honaker, Jr. & F. Morales / Emmanuel Vantieghem, Jan van Delden & Giovanni Resta. 26/5/2018

Minimal set of primes such that...

Claudio Meller / Giovanni Resta, Simon Cavegn and Michael Hürter 2/6/2018
003 Primeful Heterosquares Dmitry Kamenetsky /Claudio Meller, Michael Hürter, Emmanuel Vantieghem and Dmitry Kamenetski. 9/6/2018

Puzzles 104 & 385, revisited.

Seiji Tomita / Emmanuel Vantieghem 16/6/2018
005 Questions about the function sigma(x)=n. Fred Schneider 23/6/2018


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