It's five years since Boris Bikes/Ken Cycles/Santander Bike Hire first rolled the roads of the capital and amid the trumpeting of what a success it's been, some interesting stats are being touted about.

For example, did you know that nearly 43 million journeys have been made? Or that the most hires in one day was 73,000? Were you aware that there are 11,500 bikes for hire and 748 docking stations?

But this one fact caught our eye:

The busiest bike has been hired 4,280 times.

That's an average of 2.34 times every day for the last five years.

It turns out that every bike has a serial number on it so TfL can keep track of which docking station each bike is parked at. And, ladies and gentlemen, the serial number of London's busiest Boris Bike is... 16191

We want to find this unfailing friend to Londoners, this Samwise Gamgee of the cycle world, the Sancho Panza of pedalling — and we need your help in tracking it down.

If you spot the bicycle number 16191, tweet us a photo of it with the serial number, using the hashtag #16191. The first person to spot it will not only gain our admiration, but we'll send whatever PR stuff we can find on our desks as a thank-you.

While we may be doing something daft, TfL is letting people access the bikes for free on the weekend of 22-23 August (meaning it won't charge the £2 access fee. Provided you keep your hire periods below 30 minutes, the bikes will be free to use).