DSolve[((-2 + n)*n*(1 + n)*(3 + n) + a*x^4)*y[x] + 4*n*(1 + n)*x*Derivative[1][y][x] - 2*n*(1 + n)*x^2*Derivative[2][y][x] + x^4*Derivative[4][y][x] == 0,y[x],x]