Final answer:
The formula for the sum of the six numbers is: S = 1 + 2 + 3 + 4 + 5 + 6 = 21.
Step-by-step explanation:
The formula for the sum of the six numbers can be determined by adding the numbers together. Let's say the six numbers are: 1, 2, 3, 4, 5, and 6. The sum of these numbers would be 1 + 2 + 3 + 4 + 5 + 6 = 21. Therefore, the formula for the sum of the six numbers is: S = 1 + 2 + 3 + 4 + 5 + 6 = 21. However, one common formula used to find the sum of a set of numbers is the arithmetic series formula for a sequence of consecutive numbers, which is given by S = n/2(a1 + an), where S is the sum of the sequence, n is the number of terms, a1 is the first term, and an is the last term.
If the six numbers form an arithmetic sequence, then this formula could be used by substituting the appropriate values for a1, an, and n = 6. If other conditions apply, such as the numbers being even or fitting a different criterion from a textbook like Oxtoby, the specific formula from that context would need to be used. Without that specific information, it's recommended to refer to the textbook or notes where the formula is provided.