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 / Emmanuel Vantieghem, Giovanni Resta. 23/6/2018
006 Prime squaring the Prime square. Vic Bold / Fred Schneider, Giovanni Resta, Jan van Delden and Emmanuel Vantieghem. 29/6/2018
007 Symmetrical (Dihedral) prime tiling of the plane. Jan van Delden / Emmanuel Vantieghem. 7/7/2018
008 Primes of the migrant digit Jaime Ayala / Jan van Delden 14/7/18

Find the next term of this sequence

G. L. Honaker, Jr. 21/7/18

Find the core of a magic cube

Natalia Makarova 28/7/18

One more as 43*47=2021

Giovanni Resta 4/8/18

Magic Square 20x20

Carlos Rivera 11/8/18


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