What is the sum of the sequence:

1+3+5+7 + ... 1001

It is an arithmetic series.

The difference between consecutive terms, d, is 2

The first term, A1 = 1

The last term, An = 1001.

The formula to find the sum, S, is: S = n * (A1 + An) / 2

n is the number of terms, which is [1001 + 1] / 2 = 501

Then, S = 501 * (1 + 1001) / 2 = 251001