DSolve[Derivative[1][y][x] == (x*(-256*a*x^2 - 32*a^2*x^6 + a^3*x^12 - 256*a*x^2*y[x] + 24*a^2*x^8*y[x] + 192*a*x^4*y[x]^2 + 512*y[x]^3))/(512 + 64*a*x^4 + 512*y[x]),y[x],x]