Sum of series

∑(i=1..n) c = c·n

∑(i=1..n) i = n(n+1) / 2

∑(i=1..n) i² = n(n+1)(2n+1) / 6

∑(i=1..n) i³ = n²(n+1)² / 4

∑(i=1..n) 1/i = 1