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 Apr19 answered Approach to determining if a graph is planar by inspection/kuratowski's theorem Apr15 comment Simple maths and a typo: impossible answer? There are also solutions with $y=18$ and $y=-19$ since we then have $(2a-1)^2=13^2$ and we can have $a=7$ or $a=-6$. Feb16 answered Prove if r is the smallest positive integer such that all entries of at least one row of Sr are positive, then rad(G) = r. Jan29 answered Find all natural numbers for which $3\binom{2n}{n+1}=2\binom{2n+1}{n-1}$ holds true Jan26 revised Rank in row echelon form 1-cd not -cd+1 Jan26 revised Rank in row echelon form added 35 characters in body Jan26 answered Rank in row echelon form Dec20 awarded Constituent Dec9 awarded Caucus Dec4 comment Question on Graphs? Note that when using open neighbourhoods of vertex sets it can be awkward to have some elements of $A$ in $N(A)$ and some not in $N(A)$ as can happen with this definition. I prefer to use a definition in terms of closed neighbourhoods as follows: $N(A) := (\bigcup_{v\in A} N[v] ) \setminus A$, where $N[v]:=\{v\} \cup N(v)$. Oct17 answered Maple not displaying graph Sep8 answered Smallest non-hamiltonian k-connected graph Aug6 comment How many distinct chromatic polynomials are there for simple connected graphs? so are you looking for the numbers of different chromatic polynomials or the numbers of graphs with unique chromatic polynomials? Aug6 comment How many distinct chromatic polynomials are there for simple connected graphs? @Jernej I thought your answer was useful and may even be what Hooked was looking for, hopefully we will find out! Aug5 comment How many distinct chromatic polynomials are there for simple connected graphs? I have verified the above numbers for general graphs up to 8 vertices and for connected graphs the sequence of chromatically unique graphs is 1, 1, 2, 4, 10, 27, 100, 570. Aug5 comment How many distinct chromatic polynomials are there for simple connected graphs? The definition given at mathworld.wolfram.com/ChromaticallyUniqueGraph.html is that this sequence lists the number of graphs which have a unique polynomial, not the number of different polynomials... Jul8 comment Software to find out adjacency matrix of a graph. There are shortcuts using the underlined letters, so alt V to get to the vertex menu, etc. I've never needed edge colouring, so didn't implement it, sorry. It should be possible to add it with a bit of coding knowledge though. Jul8 comment Software to find out adjacency matrix of a graph. Sorry, no manual, but if there's something that doesn't do what you think, feel free to ask here. Jul5 awarded Yearling Jun20 revised The number of dominating sets of a bipartite graph is not exactly divisible by $2$ Tidied up the flow