A collection of $t$ sets $A_i$ is called a **t-sunflower** if $A_i \cap A_j = Z $ for all $i \neq j$ for some fixed $Z$. A well-known conjecture of Erdos and Rado says that there is a constant $C_t$ such that in any $k$-uniform family of size at least $C_t^k$ there is a $t$-sunflower. This is still wide open even for $t=3$, for more see http://en.wikipedia.org/wiki/Sunflower_(mathematics).

My question is, what is the best lower bound for $C_3$? So what is the largest known example of a $k$-uniform family that does not have a $3$-sunflower?

We can also study this as some function $f$ of $k$. I am even interested in small values, like up to $20$, if anyone can compute it. It is easy to see that $f$ is logsuperadditive. In case this is not a word, I mean $f(a+b)\ge f(a)f(b)$.

**UPDATEs.** Best currently known lower bound for $C_3$ is $\sqrt{10}\approx 3.16$, which can be found in Abbott-Hanson-Sauer: http://www.sciencedirect.com/science/article/pii/0097316572901033.

We also know $f(1)=2, f(2)=6, f(3)=20$, from some old papers, $f(4)$ might be still open.

there is a constant $C_t$ such thatin any k-uniform family of size at least $C^k_ t$..." ? $\endgroup$ – Wolfgang Apr 20 '14 at 16:53