A graph with no loops and no parallel edges is called a simple graph.
graph with no edge=$\binom{n(n-1)/2)}{0}$
graph with 1 edge=$\binom{n(n-1)/2)}{1}$
graph with 2 edge=$\binom{n(n-1)/2)}{2}$
graph with 3 edge=$\binom{n(n-1)/2)}{3}$
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graph with $n(n-1)/2$ edge=$\binom{n(n-1)/2)}{n(n-1/2}$
So total number of graph possible=$\binom{n(n-1)/2)}{0}$+$\binom{n(n-1)/2)}{1}$+$\binom{n(n-1)/2)}{2}$+....+$\binom{n(n-1)/2)}{n(n-1/2}$=$2^{n(n-1)/2}$
=$2^{n(n-1)/2}$
=$2^{6(6-1)/2}$
=$2^{6*5/2}$
=$2^{15}$