1800 1900 2100 2200 2300 2500

 

Spoiler = Hint

[hide]You won't be able to solve this without "time and date" knowledge [/hide]

Years divisible by 4 that don't/won't have a Feb 29th.

They are not leap years, despite the divisible by four rule of thumb.

 

Leap years occur in years that are exactly divisible by four, except for the years ending in 00, which are leap years only if they are divisible by 400. This is to make up for the fact that there are actually 365.242199 days in a year (according to google calculator.) and not 365.25, as is commonly thought.

Numbers - Can you spot the connection?

1800 1900 2100 2200 2300 2500

 

Spoiler = Hint

Spoiler:

You won't be able to solve this without "time and date" knowledge

 

 

Most of us will never see any of these dates.

not the best answer, but it is an answer.

The basic connection.. as stated in the question.. they are all numbers..