Two-Digit Number Sequences

nice idea but I think some are too hard and with 3 numbers only things aren't always easily 'defined' - for exmaple I think the 20th century years are too difficult and also letter numers of consecutive vowels, perhaps if you had included A it would have been easier. first day of 21st millennium is 'impossible' in my opinion; I did think of the alphabetically sorted numbers but I think 80 is missing. Also, I think perhaps all numbers should be two digits; it can be confusing to have hints that only refer to 2 digit numbers but then have some single digit numbers (eg the 1, 5.. sequence). I thought 20, 30, 50 was a Fibonacci sequence. So I like the idea but I think it needs some refining. Maybe you can have the '2-digit years' in a different column so you know you're looking for years and it still won't be too easy?

I think you should explain why each number fits, just briefly.