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Number Theory

Primes, divisibility, gcd, modular arithmetic and sequences.

经验教训

Introductory Prime factorisation Every integer is a product of primes in exactly one way. prime factorization of 360 Introductory Prime numbers Testing for primality by trial division up to the square root. is 97 prime Introductory GCD and LCM Euclid's algorithm and the identity gcd × lcm = a × b. gcd(48, 18) Core Modular arithmetic Remainders, congruences, fast powers and modular inverses. 3^100 mod 7 Introductory Divisors Counting and listing divisors from the prime factorisation. divisors of 36 Core Sequences Fibonacci, recurrences and closed forms. fib(20) Introductory Number bases Converting between decimal, binary, octal and hexadecimal. 255 to binary Core Diophantine equations Integer solutions: linear equations via Bézout, Pythagorean triples, Fermat. gcd(12, 18) Core Fermat's little theorem and Euler's theorem aᵖ⁻¹ ≡ 1 (mod p), the totient, and fast modular arithmetic. 2^100 mod 13 Advanced RSA: cryptography from number theory Public keys from two primes, and why factoring is the lock. inverse of 17 mod 3120

The mathematics of whole numbers. Some of the oldest problems and the newest cryptography live here: factor a number into primes, run Euclid's algorithm, compute huge powers modulo a prime without ever writing the power down.

更多经验教训

Real Number Systems and Number Theory

Prime and Composite NumbersThe IntegersOrder of OperationsRational NumbersIrrational NumbersReal NumbersClock ArithmeticExponentsScientific NotationArithmetic SequencesGeometric Sequences

Number Representation and Calculation

Hindu-Arabic Positional SystemEarly Numeration SystemsConverting with Base SystemsAddition and Subtraction in Base SystemsMultiplication and Division in Base Systems

Divisibility

Number theoryFundamental theorem of arithmeticEuclidean algorithmPrime numberComposite numberDivisor functionPerfect numberSieve of EratosthenesBézout's identity

Congruences

Fermat's little theoremEuler's theoremChinese remainder theoremEuler's totient functionPrimitive root modulo nQuadratic residueQuadratic reciprocityLegendre symbolMultiplicative orderWilson's theorem

Deeper water

Diophantine equationPell's equationContinued fractionPrime number theoremRiemann zeta functionDirichlet's theorem on arithmetic progressionsElliptic curveAlgebraic number theoryFermat's Last TheoremRSA (cryptosystem)Mersenne primeTwin prime

其中一些经验教训从开放文本中改编: OpenStax Contemporary Mathematics, Wikipedia. 每页课目都列出其来源和执照。

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人们对人们提出的问题

Why are primes so important?

Every integer factors into primes in exactly one way, so primes are the atoms of multiplication. Cryptography relies on that factoring being easy to state and hard to do.

How do I tell whether a big number is prime?

Trial division up to the square root works for small numbers. For large ones, probabilistic tests (Miller-Rabin) give an answer that is wrong with negligible probability, and deterministic tests (AKS) exist but are slower.

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