Assuming that 11 is the mean of the arithmetic sequence of natural numbers, there are 10 positive integers to the left, and 10 positive integers to the right.
Therefore, the sequence is:
1,2,...11,...20, 21
a₁ = 1
a₂₁ = 21
d (common difference) = 1
To solve for the arithmetic series or sum of the sequence:
S₂₁ = [tex] \frac{21}{2} [/tex] (a₁ + a₂₁)
S₂₁ = 21/2 (1 + 21)
S₂₁ = 21/2 (22)
S₂₁ = 462/2
S₂₁ = 231
ANSWER: The sum of the sequence (arithmetic series) is 231.
