A bit of background to Numberphile's first T-Shirt.
It features the first two "Brady Numbers" - 2308 and 4261.
I chose these numbers randomly at the request of Matt Parker. (see at 2'10" into video)
Matt wanted to demonstrate the Fibonnacci Sequence's link to the "Golden Ratio" is not unique.
Starting with ANY two numbers and applying the same process will also tend towards the ratio.
Following the video, the idea of Brady Numbers and a Brady Sequence captured the imagination of a few people.
I have dug out the original brown paper from that video to make the new T-Shirt.