Question 289540
The sum (S) of such a sequence is given by:
{{{S[n] = a[n]((a[1]+a[n])/2)}}} where: {{{a[1]}}} is the first term (1), {{{a[n]}}} is the nth or last term (999), so we have:
{{{S[999] = 999(1+999)/2}}}
{{{S[999] = 999(500)}}}
{{{highlight(S[999] = 499500)}}}