Soma PA até n

S_n = n(a₁+aₙ)/2.
Created by
Renato Passos, Eng. de Software
Reviewed by
Renato Passos, Eng. de Software

Last updated: Apr 18, 2026

Sₙ
155,00

Formula

S_n = n(2a₁+(n−1)r)/2

About this calculator

The arithmetic progression (AP) sum calculator up to n terms is a practical tool for quickly calculating the sum of the first n terms of an arithmetic sequence. Simply enter the first term (a₁), the common difference (r), and the number of terms (n). The calculator uses the formula S_n = n(2a₁ + (n−1)r)/2, which is equivalent to S_n = n(a₁ + aₙ)/2, where aₙ is the nth term. The result is displayed instantly, avoiding repetitive manual calculations.

The working principle is simple: the formula derives from the sum of equidistant terms, which always yields the same value. For example, in an AP with a₁=1, r=2, and n=5, the terms are 1, 3, 5, 7, 9. The sum is 25, which can be obtained by (1+9)*5/2 = 25. The calculator automates this process, being useful for students, teachers, and professionals dealing with numerical sequences.

You should use this calculator whenever you need to sum consecutive terms of an AP, such as in financial mathematics problems (simple interest), planning of increasing installments, or analysis of linear growth. It is especially useful for checking school exercises or planning budgets involving constant increases or decreases.

Important precautions: verify that the sequence is indeed arithmetic (constant difference between terms). Enter correct values for a₁, r, and n. Remember that n must be a positive integer. The formula assumes a finite AP; for infinite series, other methods are required. Avoid confusing the common difference with the general term.

Frequently asked questions

What is an arithmetic progression?

It is a numerical sequence where the difference between consecutive terms is constant. This difference is called the common difference (r). Example: 2, 4, 6, 8 has common difference 2.

Can I use the calculator if the common difference is negative?

Yes. The formula works for any common difference, positive or negative. Just ensure you enter the correct value, including the sign.

What is the difference between S_n = n(a₁+aₙ)/2 and S_n = n(2a₁+(n-1)r)/2?

The first uses the last term (aₙ), which needs to be calculated first. The second already incorporates the general term formula, being more straightforward when you know the common difference.

Can the result be a decimal?

Yes, if a₁ or r are decimals. The calculator returns the result with two decimal places by default.

How many terms can I sum?

There is no theoretical limit, but very large values may cause numerical overflow. It is recommended to use n up to 10^6 to avoid precision issues.

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