We present the discovery and characterization of a new transiting planet from Campaign 17 of the Kepler extended mission K2. The planet K2-292 b is a warm sub-Neptune on a 17 day orbit around a bright (V = 9.9 mag) solar-like G3 V star with a mass and radius of M⋆ = 1.00 ± 0.03 M⊙ and R⋆ = 1.09 ± 0.03 R⊙, respectively. We modeled simultaneously the K2 photometry and CARMENES spectroscopic data and derived a radius of Rp=2.63−0.10+0.12 R⊕ $R_{\mathrm{p}} = 2.63_{-0.10}^{+0.12}\,{R_{\oplus}}$ Rp=2.63−0.10+0.12 R⊕ and mass of Mp=24.5−4.4+4.4 M⊕ $M_{\mathrm{p}} = 24.5_{-4.4}^{+4.4}\,{M_{\oplus}}$Mp=24.5−4.4+4.4 M⊕ , yielding a mean density of ρp=7.4−1.5+1.6 g cm−3 $\rho_{\mathrm{p}} = 7.4_{-1.5}^{+1.6}\,\mathrm{g\,cm^{-3}}$ρp=7.4−1.5+1.6 g cm−3 , which makes it one of the densest sub-Neptunian planets known to date. We also detected a linear trend in the radial velocities of K2-292 ( γ˙RV = −0.40−0.07+0.07 m s−1 d−1 $\dot{\gamma}_{\textrm{RV}}= -0.40^{+0.07}_{-0.07}\,\mathrm{m\,s^{-1}\,d^{-1}}$γ˙RV=−0.40−0.07+0.07 m s−1 d−1 ) that suggests a long-period companion with a minimum mass on the order of 33 M⊕. If confirmed, it would support a formation scenario of K2-292 b by migration caused by Kozai-Lidov oscillations.