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Number Theory guides

Sorted newest first — every guide ends with practice problems and full solutions.

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Modular Arithmetic in Ten Minutes: Remainders That Solve Equations

Modular Arithmetic in Ten Minutes: Remainders That Solve Equations

Last digits, divisibility, and equations that look impossible — almost all of them collapse once you stop tracking numbers and start tracking remainders.

Number TheoryFoundation8 min read
Divisibility Rules That Save Exam Time

Divisibility Rules That Save Exam Time

Knowing why 3, 9, 11 and 7 work turns a memorised trick into a tool you can rebuild in ten seconds — including for bases and moduli nobody taught you.

Number TheoryFoundation6 min read