Ah, yes, a classic (so tempted to say, "wow never saw that before today!").

Do you think the same calculation is applicable to the HN user base? Seems like the relevant inputs are:

* New active users per month (instead of 4M born per year)

* Frequency that a link hits the HN top, assuming a high percentage of active HN users will subsequently forever know about the link

* Total number of times the link hit the top as a proxy for longevity of popularity