What is the answer to lionshead beer cap number 21?

I do not have access to real-time information, including specific details about beer bottle caps or their numbers. Therefore, I cannot provide you with the answer to Lionshead beer cap number 21.

To find this information, I recommend contacting Lionshead Brewery directly or checking their website or social media pages. They may have information about their bottle cap numbers or be able to provide you with the answer.