I'd say 78901 isn't, but that's right, 7891 isn't incrementing either. No problem, next time someone will think 109 isn't right, hopefully will read this and realize it's ok.

No, it's not and it's been already discussed before.

For decrementing sequences, 0 should come after 1, and not before 9, as in 3210.

For incrementing sequences, 0 should come after 9, and not before 1, as in 7890

There is no wrap around:

Input will always be an integer greater than 0, and less than 1,000,000,000.