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Arithmetic Sequence Calculator

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### Discrete Mathematics: Arithmetic Progressions 1. **Constant Difference**: An arithmetic sequence progresses by adding a fixed constant \(d\) to each consecutive term. 2. **Gauss's Summation.

Reviewed by Miss Saima · MA Mathematics
Last updated:
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⚙ Input Values

📊 Results

Arithmetic Sequence & Series Summary
a_20 = 98 ➔ Series Sum S_20 = 1,010 | Formula: a_n = 5n - 2 | First terms: [3, 8, 13, 18, 23, ...]
Value of the n-th Term (a_n)
a_20 = 98
Sum of First n Terms (Arithmetic Series S_n)
S_20 = 1,010 (Sum of first 20 terms)
Explicit General Formula a_n
a_n = 5n - 2
Recursive Sequence Formula
a_n = a_{n-1} + (5) with a_1 = 3
First 10 Terms of the Sequence
3, 8, 13, 18, 23, 28, 33, 38, 43, 48
✦ Algebraic Progression & Series Diagnostic
Arithmetic Progression Model (a₁ = 3 | d = 5 | n = 20): [1. Target Term Value]: The 20-th term is **a_20 = 98**. [2. Arithmetic Series Sum]: The sum of the first 20 terms equals **S_20 = 1,010**. [3. Algebraic Formulas]: Governed by the **Explicit Formula a_n = 5n - 2** and the **Recursive Definition a_n = a_{n-1} + (5) with a_1 = 3**. [4. Sequence Expansion]: First terms: **{ 3, 8, 13, 18, 23, 28, 33, 38, 43, 48, ... }**.
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📐 Formula

Arithmetic Sequence & Series equations:
General n-th Term: a_n = a_1 + (n - 1)d
Arithmetic Series Sum: S_n = (n ÷ 2)(a_1 + a_n) = (n ÷ 2)[2a_1 + (n - 1)d]
Common Difference: d = a_n - a_n-1
Recursive Definition: a_n = a_n-1 + d, a_1 = initial value

💡 Practical Example

✅

For example, finding the \(20\text{th term}\) of an arithmetic sequence starting at \ with common difference \: The \(5) = 3 + 95 = \mathbf{98}\). The sum of the first 20 terms is \ = 10 \times 101 = \mathbf{1,010}\) with explicit formula \.

📖 About Arithmetic Sequence Calculator

Discrete Mathematics: Arithmetic Progressions

  • Constant Difference: An arithmetic sequence progresses by adding a fixed constant d to each consecutive term.
  • Gauss's Summation Trick: Carl Friedrich Gauss proved that pairing terms from opposite ends of an arithmetic series yields identical constant sums enabling the closed-form summation formula \

2.

How to Use This Calculator

Enter your First Term (a₁) (e.g. 3), Common Difference (d) (e.g. 5 (step increment)), and Target Term Position to Calculate (n) (e.g. 20 (find the 20th term)). Results update instantly as you type — adjust any value to compare scenarios.

The Formula

Arithmetic Sequence \& Series equations:

General n-th Term: a_n = a_1 + (n - 1)d

Arithmetic Series Sum: S_n = (n) / (2)(a_1 + a_n) = (n) / (2)[2a_1 + (n - 1)d]

Common Difference: d = a_n - a_n-1

Recursive Definition: a_n = a_n-1 + d, a_1 = initial value

Worked Example

For example, finding the 20th term of an arithmetic sequence starting at \ with common difference The 5) = 3 + 95 = 98. The sum of the first 20 terms is \ = 10 × 101 = 1,010 with explicit formula .

Understanding Your Result

Evaluate your result in the context of your specific use case and relevant industry standards or reference values. A single calculated result is a starting point — test two to three scenarios to understand how sensitive the outcome is to your key input assumptions. For high-stakes decisions, verify your result against a secondary source or subject-matter expert before acting.

💡 Mathematical Rigor & Applied Context

  • This calculator applies exact mathematical definitions following conventions established by NIST and international standards bodies.
  • Rounding errors accumulate across multi-step calculations. For precision-critical work, maintain extra significant figures through all intermediate steps.
  • Many mathematical concepts have multiple valid formulations — if a result seems unexpected, verify which convention or definition applies to your context.
  • Dimensional analysis (unit tracking) is the fastest way to catch formula errors. Every term in an equation must have consistent, compatible units.
  • Numerical methods used in digital calculators introduce floating-point precision limits (~15 significant digits for IEEE 754 double precision).
  • For statistical and probabilistic calculations, always specify whether you are working with population parameters or sample statistics — formulas differ.
  • Visualizing a problem geometrically or testing with known boundary values (zero, infinity, negative) reveals hidden errors faster than algebraic checking.
  • When in doubt, validate your result against a simplified hand calculation or a published worked example from a textbook or standards document.

Results are for informational and educational purposes only. Always verify critical decisions with a qualified professional.

❓ Frequently Asked Questions

What is the formula for the n-th term of an arithmetic sequence?

an = a1 + (n - 1) × d, where a1 is the first term, d is the common difference, and n is the term position.

How do you find the sum of an arithmetic sequence?

Sn = n ÷ 2 × or Sn = n ÷ 2 × [2a1 + (n - 1)d].

Can the common difference (d) be negative or fractional?

Yes. A negative common difference creates a decreasing arithmetic sequence, and fractional differences create rational term sequences.

What is the difference between an arithmetic sequence and series?

An arithmetic sequence is an ordered list of numbers (e.g. 3, 8, 13, 18), while an arithmetic series is the sum of those numbers.

How do you find the common difference if you know two terms?

d = (an - ak) ÷ (n - k), where an is the n-th term and ak is the k-th term.

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