natural numbers 1 + 2 + 3 + 4 + ⋯ is a divergent series. The nth partial sum of the series is the triangular number ∑ k = 1 n k = n ( n + 1 ) 2 , {\displaystyle
4, 3, 2, 1 or 4321 may refer to: 4.3.2.1., 2010 film by Noel Clarke ...4 ..3 ..2 ..1 ...Morte, a 1967 Italian science fiction film "4, 3, 2, 1" (k-os song)
1-2-3; 1, 2, 3; or One, Two, Three may refer to: 1-2-3 (fuel station), in Norway Lotus 1-2-3, a computer spreadsheet program .123, a file extension used