[math-fun] Finding numbers represented by indefinite binary quadratic forms

Does anyone have a program for doing the following: Given an indefinite binary quadratic form ax^2+bxy+cy^2 (with discriminant b^2-4ac>0 and not a square) and a positive or negative number n, decide if ax^2+bxy+cy^2 = n has a solution. (If n = p is a prime, one can use the PARI command qfbsolve(Qfb(a,b,c),p) ) Neil