I read this book around 1983 from my school’s Jr. High Library. The main character is an android who believes he is the last one built. His maker has died and, while quite brilliant, was a very superstitious man.
The sentient android looks like a human in every way. He is the most perfect model. He had learned how to build replicas prior to his maker’s death, so he builds replicas and programs them to send him a portion of their paycheck after they blend into society. He does this for decades so he amasses great wealth, but he is lonely. Although an occasional woman shows up in his life through the years, he never connects with them. There is no one to share his life with so he starts to hunt for his siblings: the other androids made by his maker.
He finds them all (so he thinks) and none of them are a match either. Finally a woman appears and surprises him. She knows all his details. In fact, she is the random woman who has appeared to him throughout the decades. She too is an android. She explains that, yes, there were 13 androids built, but the maker was too superstitious to label an android “13.” So all these years our hero android thought he was the most advanced model, but there was one build after him. She had never revealed herself before because she believed he needed to mature