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Number Theory Terms
Terms and Definitions for Number Theory exam 1
| Term | Definition |
|---|---|
| Divisor | The number being divided into another number. Ex. b|d b is the divisor |
| Greatest Common Divsior | The largest factor in common between 2 or more given numbers. gcd(a,b) is the positive integer d satisfying d|a and d|b. If c|a and c|b then c is less than or equal to do |
| Least common multiple | Smallest positive number that is evenly divisible by 2 or more given numbers. The lcm (a,b) is the positive integer satisfying a|m and b|m. If a|c and b|c then c is greater than or equal to m |
| Relatively prime | Two or more numbers are relatively prime if and only if their gcd is 1 |
| Prime | Any number who's only factors are 1 and itself |
| Composite | Any number that has more than 2 factors |
| Congruence modulo n | If a and b are integers, we say a is equivalent to b mod n if n|(a-b) |
| Psuedoprime base a | If n is composite such that a^n = a(mod n) then n is pseudoprime to base a |
| Carmichael number | A composite number n, that satisfies a^n = a(mod n) for all n. A psuedoprime that works for any mod(n) |
| The division algorithm | Ay integer a can be divided by a positive integer b so the remainder r is smaller than b. Ex. 3|b r = 3k, 3k+1, 3k+2 |
| The Euclidean algorithm | An algorithm to compute the gcd(a,b), using modular arithmetic and back substitution |
| The fundamental theorem of arithmetic | Every positive integer n>1 is either prime or a product of primes |
| The Chinese remainder theorem | nk positive integers that are pairwise relatively prime, then x = a1(mod n1), x = a2(mod n2).. x = ak(modnk), has a unique solution (mod n1n2...nk) |
| Fermat's little theorem | P is a prime and a an integer such that p does not divide a, then a^p-1 = 1(mod p) |
| Wilson's Theorem | Any integer n>1 is prime iff (n-1)! = -1(mod n) |
| Linear congruence | a1x1 + a2x2+...anxn = b(modn) |
| Base 16 | Use mod 16 and do Euclidean algorithm |
| Binary | 1's and 0's using coefficients of powers of 2 |
| Base 10 | last digit*16^0, + next digit*16^1... |
| Mathematical induction | Assume P(n) is true, show P(1) is true, then by assuming P(n) is true, show P(n+1) is true |
| Diophantine Equation | ax+by = c with solutions x = x0+(b/d)t and y = y0 -(a/d)t |
| Binary exponentiation algorithm | Write k(am...a0)base 2 to write k as sums of powers of 2 and compute repeated squares of form a^2^m |