- quadratic-residue? a nprocedure
- a
- integer
- n
- integer
Returns #t if a is a quadratic residue modulo n, otherwise #f. The modulus n must be positive, and a must be nonnegative.
Formally, a is a quadratic residue modulo n if there exists a number x such that (* x x) = a (mod n). In other words, (quadratic-residue? a n) is #t when a is a perfect square modulo n.
Examples:
> (quadratic-residue? 0 4) #f > (quadratic-residue? 1 4) #t > (quadratic-residue? 2 4) #f > (quadratic-residue? 3 4) #f
Wikipedia: Quadratic Residue