 # Johan Wästlund

Gothenburg

http://www.math.chalmers.se/~wastlund/

I'm a researcher at Chalmers University, Gothenburg, with some bias towards discrete probability.
 2017 2016 2015 Apr 12 awarded Yearling Apr 12 awarded Yearling Apr 4 comment Guessing each other's coinsHas the 81/224-result been written down somewhere? Apr 1 awarded Curious Mar 31 asked What is the Bruss-Yor concept of no information? Dec 6 awarded Famous Question Feb 28 awarded Popular Question Jun 22 reviewed Approve suggested edit on Relaxed path decomposition of a graph Jun 21 revised For which \$n\$ is there a permutation such that the sum of any two adjacent elements is a prime?slight mathematical improvement Jun 18 reviewed Approve suggested edit on The best text to study both incompleteness theorems Jun 17 comment For which \$n\$ is there a permutation such that the sum of any two adjacent elements is a prime?Now checked up to \$N=10^{13}\$. Jun 17 answered For which \$n\$ is there a permutation such that the sum of any two adjacent elements is a prime? Jun 15 reviewed Approve suggested edit on Path connected set of matrices? Jun 12 revised For which \$n\$ is there a permutation such that the sum of any two adjacent elements is a prime?added 15 characters in body Jun 12 answered For which \$n\$ is there a permutation such that the sum of any two adjacent elements is a prime? Jun 11 comment For which \$n\$ is there a permutation such that the sum of any two adjacent elements is a prime?Never mind, by induction (and Chebyshev's theorem on primes), the graph is connected. Moreover, by the same argument it has a perfect matching, and actually two disjoint perfect matchings, which seems relevant to the question. Jun 8 comment For which \$n\$ is there a permutation such that the sum of any two adjacent elements is a prime?Does anyone have a proof that the graph (with vertices \$1,\dots,N\$ and edges where pairs of numbers sum to a prime) is connected? Equivalently, if we color the numbers \$1,\dots, N\$ red and blue in such a way that the sum of two (distinct) numbers of the same color is never prime, did we necessarily color according to parity? It seems we have to use number theory of at least the level of Chebyshev in order to show that there aren't any isolated vertices, so it can't be entirely trivial. Dec 7 reviewed Approve suggested edit on In a random graph which one is more probable, \$k\$-clique or \$k\$-core? Dec 3 awarded Nice Answer Oct 30 awarded Favorite Question