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Areas of this article contain spoilers about Double Back. Please proceed with caution.

Read at your own risk.

Double Back is the second special episode of Learningblocks. This is the 122nd Numberblocks episode overall.


It's time for a time travel adventure! Sixty-Four's new time machine keeps sending the Numberblocks back in time. Can they double up in time to fix it?



  • This episode's description used to show that it's a crossover with Alphablocks, but it was later removed.
    • This tweet from the Numberblocks Twitter gave the impression at the time that this was a mistake, and that there wasn't going to be any crossover special, at least not in the near future. However, crossover specials between Alphablocks and Numberblocks have come out since then.
  • This episode was put on iPlayer on Friday, two days before it aired on TV.
  • This episode's logo is a parody of the movie "Back to the Future".
    • Sixty-Four's time machine is a parody of the DeLorean car.
  • This episode has a time-travel plot, where a certain character travels back in time to change an event in the past.
    • The type of time-travel featured in the episode is a "time loop", where the main character gets sent back 2 minutes in the past, in an altered timeline, with the only difference being that the main Numberblock is twice their size. This repeats until Sixty-Four is the one heading to Sixty-Four's time machine, to plug the time regulator.
    • There are a total of six different timelines in the episode.
  • This is the third episode to teach about doubling and halving. First being Double Trouble and second being Snow Day Doubles.
  • This episode marks the debut of the square root sign and the decimal point.
  • Sixty-Four is the biggest Numberblock in this episode, and is the biggest Numberblock to appear in any of the specials.
  • The episode uses dynamic physics in some parts such as when Ten and Three fall into the ball pit and some of the balls roll out.
  • Despite being a special, people still refer to it as the 122nd episode of Numberblocks.
  • The shoe shop from Two Times Shoe Shop, and Octonaughty's lair from Now in 3D have cameo appearances in this episode.
  • In this episode, Three still has the rubber duck from The Lair of Shares.