Piano music courtesy of Harpeth Presbyterian Church -- used with permission.
Each state has two Senators elected for a six-year term, so each two-year cycle (a body of 50 states) means 32, 33, or 34 Senators may be up for election. 
In 2020, both Georgia seats were vacant. Georgia law required a special election, unlike Tennessee, where the vacancy is filled by Governororal appointment for that term's remainder. 
While the 20- 20 presidential winner was clear, both Senate races were a statistical tie. 
This writer is reminded of Mark Twain's words: 
“There are lies, damn’d lie's, and statistics.”