- quadratic-character a pprocedure
- a
- integer
- b
- integer
Returns the value of the quadratic character modulo the prime p. That is, for a non-zero a the number 1 is returned when a is a quadratic residue, and -1 is returned when a is a non-residue. If a is zero, then 0 is returned.
If a is negative or p is not positive, quadratic-character raises an error. If p is not prime, (quadratic-character a p) is indeterminate.
This function is also known as the Legendre symbol.
> (quadratic-character 0 5) 0 > (quadratic-character 1 5) 1 > (quadratic-character 2 5) -1 > (quadratic-character 3 5) -1
Wikipedia: Legendre Symbol