I have an old bank account. I am trying to find out if it's still open. I only have the account number, and no memory of the bank. How can I figure out which bank my account number belongs to??
You will probably not be able to figure out the bank from the account number. You can check for your name on registries of abandoned bank accounts or unclaimed money, but without more information, you don't have a lot of options.
Every bank has uses their own number ranges and assigns account numbers as they like. That means that the same account number could be in use by basically every bank simultaneously - which makes it impossible to find out the bank from the account number.
A similar situation would be to find a street name from the house number - obviously, there are many streets that have a given number.