You can do a regex check for "all digits the same":
^(\d)\1*$
But for the rest you are much, much better off checking the entered value against a list of valid account numbers = while you can very easily write javascript code to check for a rising or falling number sequence that doesn't eliminate accounts where two numbers have been swapped or "just typed wrong" - that's why credit card numbers and even bank account numbers include checksum data to validate "this is a correct account number and it's one of ours" without going to a database. Checking the checksum should eliminate all digits the same as well!
And that is the final and pretty much essential step: validate the account number against a list of "actual accounts" in a DB to be sure the number is correct, valid, and the account is not blocked, frozen, or closed.