Answer:
502503
Step-by-step explanation:
formula is
Sn = n/2 * (2a1 + (n - 1 ) * d)
S is the sum
a1 is the first number which is 1
d is the difference between each number
n is the last number of terms
S1002 = 1002/2 * ((2 * 1002) + (1002 - 1) * 1002) = 502503
