  Topological physics opens a door towards flexible routing and resilient
localization of waves of various nature. Recently proposed higher-order
topological insulators provide advanced control over wave localization in the
structures of different dimensionality. In many cases, the formation of such
higher-order topological phases is governed by the lattice symmetries, with
kagome and breathing honeycomb lattices being prominent examples. Here, we
design and experimentally realize the resonant electric circuit with $D_4$
symmetry and additional next-nearest-neighbor couplings. As we prove, a
coupling of the distant neighbors gives rise to an in-gap corner state.
Retrieving the associated invariant directly from the experiment, we
demonstrate the topological nature of the designed system, revealing the role
of long-range interactions in the formation of topological phases. Our results
thus highlight the distinctions between tight-binding systems and their
photonic counterparts with long-range couplings.
