Sequence Calculator

Calculate arithmetic, geometric, Fibonacci, and custom sequences. Find nth terms, sums, and analyze convergence with step-by-step solutions.

Use: n, +, -, *, /, ^, sin(n), cos(n), ln(n), sqrt(n), factorial(n)
Enter the general term aₙ as a function of n

Sequence Types & Formulas

A sequence is an ordered list of numbers following a specific pattern or rule. Each number in the sequence is called a term.

Arithmetic Sequences

General Term: $a_n = a_1 + (n-1)d$
Sum Formula: $S_n = \frac{n}{2}[2a_1 + (n-1)d]$ or $S_n = \frac{n}{2}(a_1 + a_n)$

In an arithmetic sequence, each term differs from the previous by a constant value (common difference d).

Example: 2, 5, 8, 11, 14, ... (d = 3)

Geometric Sequences

General Term: $a_n = a_1 \cdot r^{n-1}$
Sum Formula: $S_n = a_1 \frac{1-r^n}{1-r}$ (r ≠ 1)
Infinite Sum: $S_\infty = \frac{a_1}{1-r}$ (|r| < 1)

In a geometric sequence, each term is obtained by multiplying the previous term by a constant ratio r.

Example: 3, 6, 12, 24, 48, ... (r = 2)

Fibonacci Sequence

Recursive: $F_n = F_{n-1} + F_{n-2}$ with $F_1 = F_2 = 1$
Binet's Formula: $F_n = \frac{\phi^n - \psi^n}{\sqrt{5}}$
Golden Ratio: $\phi = \frac{1+\sqrt{5}}{2} \approx 1.618$

Each Fibonacci number is the sum of the two preceding ones. The ratio of consecutive terms approaches the golden ratio.

Sequence: 1, 1, 2, 3, 5, 8, 13, 21, 34, ...

Convergence of Sequences

Definition: $\lim_{n \to \infty} a_n = L$ (if limit exists)

A sequence converges if its terms approach a specific value as n approaches infinity.

Convergent Examples:
  • $a_n = \frac{1}{n}$ → 0
  • $a_n = \frac{n+1}{n}$ → 1
  • $a_n = \frac{(-1)^n}{n}$ → 0
Divergent Examples:
  • $a_n = n$ → ∞
  • $a_n = (-1)^n$ (oscillates)
  • $a_n = 2^n$ → ∞

Common Sequence Types

Type Formula Example
Natural Numbers $a_n = n$ 1, 2, 3, 4, ...
Perfect Squares $a_n = n^2$ 1, 4, 9, 16, ...
Powers of 2 $a_n = 2^n$ 2, 4, 8, 16, ...
Factorials $a_n = n!$ 1, 2, 6, 24, ...
Harmonic $a_n = \frac{1}{n}$ 1, 1/2, 1/3, 1/4, ...

Sequence Tip:

When analyzing a sequence, look for patterns in differences between consecutive terms, ratios of consecutive terms, or try to express the nth term as a function of n.

Sequence Examples

Arithmetic Sequence
2, 5, 8, 11, 14, ...
First term: 2, Common difference: 3
Geometric Sequence
1, 0.5, 0.25, 0.125, ...
First term: 1, Common ratio: 0.5
Fibonacci Sequence
1, 1, 2, 3, 5, 8, 13, ...
Each term is sum of previous two
Convergent Sequence
1, 1/2, 1/3, 1/4, ...
Converges to 0

Sequence Calculator Answers

What does the sequence calculator do?

The sequence calculator helps you find terms in a mathematical sequence, such as arithmetic or geometric sequences, based on the given formula or initial terms.

What types of sequences can it calculate?

It can compute arithmetic, geometric, harmonic, Fibonacci, and custom-defined sequences by identifying patterns and generating terms accordingly.

Can it find a specific term in the sequence?

Yes. You can input the position of the term you want, and the calculator will compute its value based on the rule or formula you provide.

Is it useful for students?

Definitely. It’s great for students learning about sequences and series in algebra or pre-calculus, helping them check their work and understand patterns.

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