Large Transport
Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Deviation / Discrepancy - Procedural Landing Without Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Flight Crew Became Reoriented
Human Factors
I was performing Pilot Monitoring (PM) duties.  We were being vectored for a visual to runway 17R. At approximately 9;000 feet and 17 NM from airport we called the airport in sight.  Approach cleared us for visual approach and to contact the tower 133.3 at JOULE.  Pilot Flying (PF) set 6;000 feet in Flight Control Panel (FCP) and initiated level change.  I had assumed that we were going to join the glideslope from our current altitude so I was surprised that we were going to start a descent immediately.  However; I had no concerns about terrain clearance since it was day VMC conditions and the terrain is very flat northeast of the airport.  I failed to recognize that 6;000 feet was not appropriate relative to the airport elevation in DEN.  Later I learned that the PF's intention was to set the appropriate altitude for JOSEE (the fix prior to JOULE) which should have been 8;000 feet. What did occur to me and served as a major distraction was the thought that if we started down now that we might descend below the DEN Class B airspace.  I took a few moments to reference the DEN Class B chart on the EFB.  By the time I looked back at the flight instruments; we were at approximately 6;500 feet.  The PF had realized that we were low for the approach and leveled off.  At the same time; approach control issued a precautionary low altitude alert.  I saw that we were now level and safe relative to terrain so I responded that we still had the airport in sight.  The surprise and timing of that call caused a further distraction that resulted in us failing to call the tower at JOULE as previously instructed.  At 500 feet I was so focused on making sure that we were stable and where we needed to be that I automatically called 'Stable; cleared to land' without realizing that our last transmissions had been with approach and not tower.  We landed on 17R without incident.  I never heard any attempts to call us on either the approach frequency or Guard frequency.  After clearing the runway we discovered that we had not contacted tower.  We called ground control and received clearance to ramp.  After block in; the Captain called Denver tower and was told that they had issued us a landing clearance and a green light (I am assuming light gun signal although I never saw it).  They stated that they had no issues with our flight.  The PF selected an inappropriate altitude on FCP and PM failed to identify and capture the error.My intention was to be flexible with the PF's plan to execute the visual approach.  Once I realized that we were going to start an immediate descent; I tried to quickly adapt and make sure that we stayed legal.  But I allowed myself to be distracted with a relatively minor issue at the expense of not backing up the PF on the much more important issue of selecting an appropriate altitude to descend to initially.
A First Officer reported that the pilot flying descended to an unsafe altitude on a visual approach in to DEN. After becoming reoriented; the flight landed without making contact with the tower.