What is the sweet spot for notification frequency?

Every app owner wants users to remember that their app exists and obviously use their app. There is a handshake agreement when the user opts in to receive notifications that they want more interactivity from the experience. But what is the boundary when the notifications become too bothersome and users turn them off out of avoidance? Does anyone have any experience with this? I was thinking of having a weekly reminder if the user hasn't opened the app in 7 days - is this a sweet spot or is this already too often? The research shows that it is completely based on perceived value of the notification, but in general the advice is less than 5 times a week which seems obvious.