Encrypted and factory reset - Do I need to decrypt device? We can remove data permanently from android flash memory, which is encrypted, after a factory reset. 

After doing this, do we need to decrypt the device for using it again or factory reset the device?
It is in the default factory reset state ( like a new device ). You can't decrypt the device even if you wish to as the encryption password (generated from a combination of user lock screen PIN and encryption algorithm ) is lost

From Android's Factory Reset Does Not Wipe Your Data: Here's The Solution


  Encrypting does not completely delete the files, but the factory reset process gets rid of the encryption key. As a result, the device has no way it can decrypt the files and, therefore, makes data recovery extremely difficult.