Arithmetic and Geometric Sequences
Khan Academy
Khan Academy's Algebra 1 unit on sequences, with videos and exercises on recursive and explicit formulas. After working through it a student can extend a sequence, write its formula, and evaluate any term.
More resources on Sequences & Series
Wolfram MathWorld
MathWorld is an online mathematics encyclopedia from Wolfram Research offering detailed, browsable articles on topics across the math spectrum, including algebra, geometry, calculus, and number theory. Each entry includes definitions, theorems, formulas, diagrams, worked examples, and links to further reading.
Calculus II: Series & Sequences
Chapter of Paul Dawkins's free Calculus II notes covering sequences, infinite series, partial sums, the integral, comparison, alternating, ratio and root tests, absolute convergence, power series and Taylor series, with worked examples. Learners can decide convergence and represent functions as power series.
Art of Problem Solving Wiki - Sequences
A reference entry from the Art of Problem Solving wiki defining sequences, recursion, and common families, with linked competition problems. Useful for olympiad and contest preparation once the basic definitions are already familiar.
Sequences and Series
Brilliant's interactive course built around problem sets covering arithmetic and geometric progressions, recursion, and summation techniques. Learners practise pattern-finding and closed-form summation by solving rather than by reading proofs.
Introducción al cálculo
Spanish-language course from the Universitat Autònoma de Barcelona that reviews numbers and functions, polynomial, exponential, logarithmic and trigonometric functions, then introduces differentiation, integration and complex numbers. Prepares students for a first-semester university calculus course in science or engineering.
Introduction to Complex Analysis
Wesleyan University course on complex analysis covering complex numbers, analytic functions, conformal mappings, Möbius transformations, contour integration, Cauchy's theorem, power and Laurent series, and residues. Learners finish able to evaluate contour integrals and analyze complex-differentiable functions.