This story, dead-tree, is set during the times when banks had blank deposit slips in the lobby and you could write your own account number on the slips and use them to deposit money.
Maybe some banks still use them, but I haven't seen any of them for years.
In this story, about all I remember is that the main character used those slips to fill in a bank account number (not sure if it was his own), then when other people who came into the bank used those slips and, unknowingly, deposited their money into his account, he grew rich. I believe, but am not sure, that he then transferred the money to some overseas place that was untouchable by U.S. government.
I thought it might be a Paul Erdman book but I went through his novels on goodreads and not one of them rings a bell.
Anybody have a clue?