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
002

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
004

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
009

Find the next term of this sequence

G. L. Honaker, Jr. / Dmitry Kamenetsky and Antoine Verroken. 21/7/18
010

Find the core of a magic cube

Natalia Makarova / Unsolved 28/7/18
011

One more as 43*47=2021

Giovanni Resta / Unsolved 4/8/18
012

Magic Square 20x20

Carlos Rivera / Tognon Stefano 11/8/18
013

The set {a+m,a+2m,...} contains infinitely...

Emmanuel Vantieghem / John Arioni, Jan van Delden 18/8/18
014

Prime cluster in Euler's trinomial

Shyam Sunder Gupta / Unsolved 15/8/18
015

Consecutive primes and Pandigitals

Rodolfo Kurchan / Jeff Heleen, Claudio Meller and Emmanuel Vantieghem 1/9/18
016 "Good residues" r mod p Jaroslaw Wroblewski / Yilin Zhang 8/9/18
017

The square of Prime contains Prevprime

Paolo P. Lava / Unsolved 15/9/18
018

Prime repunits as sum of consecutive primes

Claudio Meller / Hans Havermann 22/9/18
019 m +/-2^k+/-1 integers. Arkadiusz Wesolowski / Unsolved 29/9/18
020

Another puzzle on consecutive primes.

Zak Seidov / Unsolved 6/10/18

 


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