Jest na to wzór
[tex] \frac{x \times (x + 1)}{2}[/tex]
Zatem
[tex] \frac{366 \times 367}{2} = \frac{134322}{2} = 67161[/tex]
Lub inny wzór
[tex]Sn = \frac{a1 + an}{2} \times n[/tex]
Zatem
[tex]Sn = \frac{1 + 366}{2} \times 366 \\ \frac{367}{2} \times 366 = 183.5 \times 366 = 67161[/tex]