: People created absurd logical loops to "prove" the kid was actually a genius and that 9 + 10 really does equal 21.

original sound - soundeffectpack ... Stupid? No, not. What's 9 + 10? 21, you stupid. TikTok·althea420

Even after the Vine app shut down in 2017, the meme lived on through:

The dialogue that launched a thousand remixes went like this: "You stupid." Kid: "No I'm not." Brother: "What's 9 plus 10?" Kid: (Without a second's hesitation) " 21 ." Brother: "You stupid." Why It Became a Legend