4
Problems(2)
a 2-connected graph has an extra vertex
Source: 239 2000 S4
5/18/2020
A graph is called 2-connected if after removing any vertex the remaining graph is still connected. Prove that for any 2-connected graph with degrees more than two, one can remove a vertex so that the remaining graph is still 2-connected.
graphgraph theoryConnected graphsConnectivitycombinatorics
30-digit number with any 5 consecutive digit divisible by 13
Source: 239 2000 J4
5/17/2020
Is there a 30-digit number such that any number formed by its five consecutive digits is divisible by 13?
number theory