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IntegerMathUtils.jl

This library adds several functions useful for doing math on integers. Machine integers (and any other non-BigInt Integer type) use native Julia algorithms; BigInt inputs use GMP.

Functions

  • iroot(x::Integer, n::Integer) the integer nth root of x, truncated toward zero: for x >= 0 the largest integer a such that a^n <= x, and iroot(-x, n) == -iroot(x, n) for odd n (e.g. iroot(-9, 3) == -2). Throws a DomainError for n <= 0 or an even root of a negative number.
  • rootrem(x::Integer, n::Integer) returns (iroot(x, n), x - iroot(x, n)^n).
  • ispower(x::Integer) returns whether there are integer base and exponent > 1 values such that base^exponent == x. For negative x only odd exponents count, so ispower(-8) == true but ispower(-4) == false. 0 and ±1 are perfect powers.
  • find_exponent(x::Integer) returns the largest possible integer exponent such that base^exponent == x for some base (only odd exponents for negative x). Returns 1 for x ∈ [-1, 1].
  • is_probably_prime(x::Integer; reps=25) returns if x is prime. Will be incorrect less than 4^-reps of the time.
  • kronecker(a::Integer, n::Integer) Computes the Kronecker symbol which is a generalization of the legendre and jacobi symbols.