>On the 1st day of Xmas, my true love gave to me:
>1 item
>On the 2nd day of Xmas, my true love gave to me:
>2 items + 1 item
>On the 3rd day of Xmas, my true love gave to me:
>3 items + 2 items + 1 item
>.
>.
>On the n-1 day of Xmas, my true love gave to me:
>n-1 items + n-2 items + ... + 1 item
>On the nth day of Xmas, my true love gave to me:
>n items + n-1 items + ... + 1 item
>
>How many total items did my true love give to me, as a function of n?

Number of gifts = gifts(n)

FUNCTION gifts(n)
lnReturn = 0
FOR I = 1 TO n
  FOR H = 1 TO I
    lnReturn = lnReturn + H
  ENDFOR
ENDFOR
RETURN lnReturn

not arithmetic, but it works