Let $L$ be a finite lattice with least element $\hat{0}$, greatest element $\hat{1}$, and Möbius function $\mu$.

*Question 1*: What class of lattices the following property characterizes? $$\mu(\hat{0},a)=\mu(\hat{0},\hat{1})\mu(a,\hat{1}), \ \forall a \in L$$ It follows that $\mu(\hat{0},\hat{1}) = \pm1$.

*Remark*: It is satisfied by any boolean lattice, more generally by the face lattice of any convex polytope (as suggested by John Shareshian), and more generally by any [Eulerian lattice][1].    
*Proof*: An Eulerian lattice is a graded lattice $L$ such that for any $a,b \in L$ with $a \le b$, we have $\mu(a,b)= (-1)^{|b|-|a|} $, with $a \mapsto |a|$ the rank function. The result is immediate. $\square$   

*Question 2*: Is there a non-Eulerian lattice with the above property on the Möbius function?  
**Yes**, see the answer of John Machacek.  

As suggested by Sam Hopkins:    
*Question 3*: Is there a non-Eulerian *atomistic* lattice with the above property on the Möbius function? 

 


  [1]: https://en.wikipedia.org/wiki/Eulerian_poset