Which is of considerable importance in applied mathematics. Functions satisfying this differential equation are called Legendre functions (of order n). When n is a nonnegative integer, the equation has polynomial solutions of special interest called Legendre polynomials. Legendre’s name is also associated with the symbol (c|p) of number theory. The Legendre symbol (c|p) is equal to ±1 according as the integer c, which is prime to p, is or is not a quadratic residue of the odd prime p. (For example, (6|19) = 1 since the congruence x2 ≡ 6 (mod 19) has a solution, and (39|47) = -1 since the congruence x2 ≡ 39 (mod 47) has no solution.)