\[ -a x-b \sin (x)-c \cos (x)+y^{(n)}(x)+2 y^{(3)}(x)+y'(x)=0 \] ✓ Mathematica : cpu = 0.682601 (sec), leaf count = 80
\[\left \{\left \{y(x)\to \frac {a x^2}{2}+\sin (x) \left (-\frac {3 b x}{8}-\frac {c x^2}{8}+c_2 x+\frac {13 c}{16}+c_1+c_4\right )+\cos (x) \left (\frac {1}{16} b \left (2 x^2-9\right )-\frac {5 c x}{8}-c_4 x+c_2-c_3\right )+c_5\right \}\right \}\]
✓ Maple : cpu = 0.414 (sec), leaf count = 69
\[ \left \{ y \left ( x \right ) ={\frac { \left ( b{x}^{2}+ \left ( -4\,c-8\,{\it \_C4} \right ) x-6\,b-8\,{\it \_C2}+8\,{\it \_C3} \right ) \cos \left ( x \right ) }{8}}+{\frac { \left ( -c{x}^{2}+ \left ( -4\,b+8\,{\it \_C3} \right ) x+6\,c+8\,{\it \_C1}+8\,{\it \_C4} \right ) \sin \left ( x \right ) }{8}}+{\frac {a{x}^{2}}{2}}+{\it \_C5} \right \} \]