Six to Ten discover they are all Five-and-a-friend.
Story
Numberblocks 1-5 get an invitation reading that they're invited to a five-star ball at the Two Palms Dance Floor. Two wonders where it is.
Meanwhile at the ball, Numberblocks 6-10 start dancing, but they can't start without Five. They then discover that they have a five. Six is 5+1, Seven is 5+2, Eight is 5+3, Nine is 5+4, and Ten is 5+5.
Now, One, Two, Three, Four, and Five are at the ball, and there are five Fives there, but where are 6-10? Everyone starts searching for them, while the other Numberblocks 1-5 come to the ball. But where are Six, Seven, Eight, Nine, and Ten? One decides they should add up.
5 + 1 = 6
5 + 2 = 7
5 + 3 = 8
5 + 4 = 9
5 + 5 = 10
But where are One, Two, Three, Four, and Five? 6-10 notice they have a sparkly band above their fifth block. They separate into the five Fives and 1-5. They still haven't found 6-10, so they start looking.
The other 1-5 still haven't found 6-10. They add up to 6-10 again, but where are 1-5? They separate their blocks, but 1-5 continue searching for 6-10.
The other 1-5 still haven't found 6-10. They add up to 6-10 again, but where are 1-5? They separate their blocks, before the other 1-5 come to them quickly. They ask each other: "Where, oh, where are six to ten?!" Numberblocks 6-10 appear again and they all get the party started.
Trivia
Song: High Five (version 2)
Everyone stays vertical in this episode, except for Four in the beginning.
This is the first time there are seven fives.
The five Fives would've been called the Five Star Fives in this episode.
This is the first time the Numberblock's numberling number of the said Numberblock forms without their square root (5^2=25).
The 1-5 that returned were the ones which 6 through 10 first split up into at the end.
Eight's middle arms are used to split the first time, but not the second.
Running gags:
1-5 wondering where 6-10 are, and 6-10 wondering where 1-5 are.
Six saying: "Let's get this party started!"
Nine shouting: "HOLD ON!"
The third time 1-5 add up with the five Fives, Five, now having gone insane, shouts in a not normal five-voice: "FIVE AND ANOTHER FIVE!".
All of the Numberblocks (including 4) stand tall in this episode.
References
The five Fives saying “to the side, up above, down low, too slow” is a reference to the Season 1 episode Five.
Numberblocks 1, 2, 3, 4, and the six 5s saying “Where oh where are Six to Ten?” is a reference to Holes.