Contrary to popular (at the time) belief, the "20" in "VIC-20" wasn't actually a reference to any part of the system. Speculation varied, from it being a reference to its horizontal text resolution (which was actually 22 columns), the total size of the system memory (16KB of ROM and 5KB of RAM, for 21KB total), revision numbers, IC count (the original version had 32 chips, the "CR" or D version had 26; both had 7 proprietary chips), speed references or all manner of other potential origins.
As it turns out, however, it was much less meaningful. According to Michael Tomczyk (responsible for leading development on the VIC-20), in an interview in 1996, 20 was simply chosen as it was "a friendly number" to offset that VIC "sounded like a truck driver". It was, after all, "the friendly computer".
