We found that there is a remarkable relationship between the triangular numbers $T_k$ and the astronomical clock (horologe) of Prague. We introduce Šindel sequences $\left\{a_i\right\}\subset \mathbb{N}$ of natural numbers as those periodic sequences with period $p$ that satisfy the following condition: for any $k\in \mathbb{N}$ there exists $n\in \mathbb{N}$ such that $T_k=a_1+\cdots +a_n$. We shall see that this condition guarantees a functioning of the bellworks, which is controlled by the horologe. We give a necessary and sufficient condition for a periodic sequence to be a Šindel sequence....