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Number Sequence Calculator

Identify, extend, and analyse arithmetic, geometric, Fibonacci, and other number sequences. Find the nth term and partial sums.

Identify & Extend a Sequence

Enter the known terms of your sequence (at least 3), separated by commas.

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Generate a sequence

Type
First term (a₁)
Common diff/ratio
Number of terms
Analysis Result
Sequence Type
Arithmetic
aₙ = 2 + (n−1)×3
PropertyValue
Extended Sequence

Term Table

nTerm (aₙ)Partial Sum (Sₙ)

Types of Number Sequences

TypeDefinitionFormulaExample
ArithmeticConstant difference (d)aₙ = a₁ + (n−1)d2, 5, 8, 11, …
GeometricConstant ratio (r)aₙ = a₁ × rⁿ⁻¹2, 6, 18, 54, …
FibonacciEach term = sum of previous twoaₙ = aₙ₋₁ + aₙ₋₂1, 1, 2, 3, 5, 8, …
TriangularCount of dots in triangleaₙ = n(n+1)/21, 3, 6, 10, 15, …
SquarePerfect squaresaₙ = n²1, 4, 9, 16, 25, …

Sum Formulas

Arithmetic series: Sₙ = n/2 × (a₁ + aₙ) = n/2 × (2a₁ + (n−1)d)
Geometric series (r≠1): Sₙ = a₁ × (1−rⁿ)/(1−r)
Infinite geometric series (|r|<1): S∞ = a₁/(1−r)