A linear number sequence is also known as an arithmetic sequence. It's a sequence of numbers such that the difference between consecutive terms is constant. This constant difference is called the step or common difference ($d$).

Sum Formula:

$$ S_n = \frac{n}{2}(a_1 + a_n) $$

Where:

• $S_n$ is the sum of the sequence.
• $n$ is the total number of terms.
• $a_1$ is the first term (Start Number).
• $a_n$ is the last term in the sequence.

The number of terms, $n$, is calculated as: $n = \lfloor \frac{a_{n, \text{end}} - a_1}{d} \rfloor + 1$. The calculator finds the last term ($a_n$) that is less than or equal to the end number you provide.