\\ return one non-trivial divisor of n > 1 using Shanks's SQUFOF squfof(n) = { if (isprime(n) || issquare(n, &n), return(n)); p = factor(n,0)[1,1]; if (p != n, return(p)); if (n%4==1, D = n; d = sqrtint(D); b = (((d-1)\2) << 1) + 1 , D = n << 2; d = sqrtint(D); b = (d\2) << 1 ); f = Qfb(1, b, (b^2-D)>>2); l = sqrtint(d); q = []; lq = 0; i = 0; while (1, i++; f = qfbred(f, 3, D, d); a = component(f, 1); if (!(i%2) && issquare(a, &as), j = 1; while (j<=lq, if (as == q[j], break); j++ ); if (j > lq, break) ); if (abs(a) <= l, q = concat(q, abs(a)); print(q); lq++; ) ); print("i = ", i); print(f); bb = component(f, 2); gs = gcd([as, bb, D]); if (gs > 1, return (gs)); f = Qfb(as, -bb, as*component(f,3)); g = qfbred(f, 3, D, d); b = component(g, 2); until (b1 == b, b1 = b; g = qfbred(g, 3, D, d); b = component(g, 2); ); a = abs(component(g, 1)); if (a % 2, a, a>>1); }