Welcome to the forum.
You have a Harrington & Richardson Arms Co.
Model 1900 single barrel shotgun. The partial numbers are the patent dates: Feb. 20 & 27 1900
. That model is broken down by lifting the swivel tab on the hinge pin and turning it 1/4 turn counter-clock-wise, then pulling it out. The "splinter" type forestock is attached to the barrel by a screw. Serial number to date of manufacture is not known, at this time, but your gun was probably made in the 1909 - 1911 time frame.
Depending upon condition - current RETAIL value will vary from about $35 for a poor example to around $150 for a v.good example. Unused or new examples may exist and if they do they would be desireable collector items worth in excess of $200.
These guns were made to handle early smokeless or semi-smokeless low power loads and did not have "self-adjusting" latching systems so many are seen shot loose. I, personally, would retire the old girl - she has earned it.