Nth-term and finite-sum calculator

Arithmetic Sequence Calculator

Find the nth term and sum of an arithmetic sequence from its first term, common difference, and term number.

All entries and results stay in this browser tab. Nothing is uploaded, persisted, placed in the URL, or sent to analytics.

Enter known values

First term a₁Common difference dTerm number n

n must be a positive whole number no greater than 1,000,000,000. The page previews at most 20 terms.

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Method

The nth term uses aₙ = a₁ + (n − 1)d. The finite sum is independently evaluated as Sₙ = n(a₁ + aₙ)/2. Numeric inputs use finite JavaScript double precision and results are displayed with controlled significant digits.

Limitations

V1 supports the first-term/common-difference mode only. It does not infer a sequence from arbitrary terms or handle geometric, recursive, polynomial, Fibonacci, or infinite series. The term preview is capped at 20 and n at one billion.

Privacy

No account, server calculation, remote API, fetch, XHR, beacon, cookie, local storage, session storage, IndexedDB, or user-value telemetry is used.