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Arithmetic Sequence Calculator.

Calculate the nth term and sum of an arithmetic sequence.

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Set your values

Results update as you type.

Nth term: 29

Nth term

29.000000
Sum: 155

Sum

155.000000

Results update automatically as you type.

Use Cases

Find any term in a sequence

Quickly determine the value of a specific term in an arithmetic progression without manually listing all previous terms.

Example: Find the 20th term of the sequence starting at 5 with a common difference of 3.

Calculate the sum of a series

Compute the total of the first n terms of an arithmetic sequence, useful for financial planning or mathematical problems.

Example: Sum the first 15 terms of the sequence 10, 7, 4, ...

Frequently Asked Questions

What is an arithmetic sequence?
An arithmetic sequence is a list of numbers where the difference between consecutive terms is constant. This constant is called the common difference. For example, 2, 5, 8, 11 is an arithmetic sequence with a common difference of 3.
How do I find the nth term of an arithmetic sequence?
The nth term is found using the formula: a_n = a_1 + (n - 1) * d, where a_1 is the first term, d is the common difference, and n is the term number. Simply enter these values into the calculator to get the result.
How is the sum of an arithmetic sequence calculated?
The sum of the first n terms is calculated using the formula: S_n = n/2 * (2a_1 + (n - 1) * d) or equivalently S_n = n/2 * (a_1 + a_n). The calculator uses the first term, common difference, and term number to compute this sum automatically.

Tips & Common Mistakes

Tips

  • Ensure the common difference is consistent: subtract any term from the next to verify it matches.
  • If the common difference is negative, the sequence decreases; the calculator handles negative values correctly.
  • Use the term number as a positive integer; the calculator assumes n is a whole number.
  • Double-check your inputs: the first term and common difference can be decimals or fractions.

Common Mistakes to Avoid

  • Confusing the term number with the index: the first term corresponds to n=1, not n=0.
  • Entering the common difference as the second term instead of the difference between terms.
  • Using the wrong sign for the common difference when the sequence decreases.

Last updated: August 13, 2026