A block in a graph is a maximal connected subgraph that has no cut-vertex. A complete graph having $n$ nodes is denoted by $K_n$. A block graph is a graph in which each block is a complete graph. For example in figure a block graph with blocks $K_2,K_2,K_3,K_4 $ and $K_5$. What is the number of non-isomorphic block graphs on $n$ nodes?. 
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$\begingroup$ You mean, "What is the number of non-isomorphic block graphs on $n$ nodes?", right? $\endgroup$ – Alex Suciu May 14 '17 at 12:01
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$\begingroup$ Now I have edited it. $\endgroup$ – Ranveer Singh May 14 '17 at 13:02
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This appears to be http://oeis.org/A035053 . References and formulae are there.
answered May 14 '17 at 12:54
