Maybe you can look into numbers relating to his most well-known movies. Either their names or when they were released.
Popeye, Hook, Ms. Doubtfire, The Fisher King, The Birdcage, Jumanji, Aladdin, and of course many more.
Many of his movie titles themselves seem to relate to something of a dark occult sacrificial nature.
I'm not to familiar with the nature of his death. One of the strangest phenomenons was his role in World's Greatest Dad, in which he played the father of a son who died of a humiliating "autoerotic asphyxiation" while viewing pornography alone in his room at night. The entire plot was based around the father lying about the nature of his son's death by writing a poetic suicide note that went viral, and telling people made-up stories that he thought would be easier for people to stomach than the truth. It was said that Robin wanted to make this film because he developed a deep emotional attachment for people who suffered from this specific type of suicide/accident.
I have already analyzed every single movie he ever did, including co-stars, directors, release dates and cross-checked them with the opening of the Golden gate bridge, the day when the Golden Gate entered 266°, 72 years later when the Golden Gate entered 267°, the Golden Gate tetrad midpoint, the September Eleven attacks and a couple of other events. I have also checked his advertisements, his video clips (Don't Worry, Be Happy). Besides the obvious symbolism, there are many magic numbers and Golden Gate numbers among them. I hope to post more about it bit by bit.
Robin Williams died very similar like the boy in "World's Greatest Dad", with t a belt around his neck hanging from a door knob. No autoerotic stuff was reported though.
Stay tuned for more!