Arithmetic Sequence Calculator
Find the nth term and the sum of an arithmetic sequence.
What is Arithmetic Sequence?
An arithmetic sequence adds the same amount at every step: 3, 7, 11, 15, … with a common difference of 4. The nth term is a₁ + (n − 1)d and the sum of the first n terms is n times the average of the first and last — which is why the total can be found without adding the middle values at all.
How it works
Both answers are closed forms, so any length up to a million is instant and the page never has to build a giant list to sum it. The substituted working is printed as a separate step because the substitution is what is being learned here — the arithmetic is the easy part. Negative and fractional differences are ordinary input rather than special cases.
- Enter your input. Type or paste your input into the field above — the tool responds instantly.
- Review the result. Output updates live as you type. Everything runs entirely in your browser.
- Copy or download. Use the Copy button to grab the result, or Download to save it as a file.
Examples
Realistic sample
Type or paste any realistic input — the tool computes the result locally and instantly.
Common mistakes
Expecting a server round-trip
Nothing is uploaded — every tool in this category runs entirely in your browser.