<math xmlns='http://www.w3.org/1998/Math/MathML'><semantics><mrow xref='id18'><mrow xref='id16'><mrow><mo>-</mo><mrow xref='id5'><mi xref='id1'>n</mi><mo>⁢</mo><mrow xref='id4'><mi xref='id2'>u</mi><mo>⁡</mo><mfenced><mi xref='id3'>n</mi></mfenced></mrow></mrow></mrow><mo>+</mo><mrow xref='id15'><mfenced><mrow xref='id9'><mrow xref='id7'><mo>-</mo><mi xref='id6'>n</mi></mrow><mo>-</mo><mn xref='id8'>2</mn></mrow></mfenced><mo>⁢</mo><mrow xref='id14'><mi xref='id10'>u</mi><mo>⁡</mo><mfenced><mrow xref='id13'><mi xref='id11'>n</mi><mo>+</mo><mn xref='id12'>2</mn></mrow></mfenced></mrow></mrow></mrow><mo>=</mo><mn xref='id17'>0</mn></mrow><annotation-xml encoding='MathML-Content'><apply id='id18'><eq/><apply id='id16'><plus/><apply><minus/><apply id='id5'><times/><ci id='id1'>n</ci><apply id='id4'><ci id='id2'>u</ci><ci id='id3'>n</ci></apply></apply></apply><apply id='id15'><times/><apply id='id9'><minus/><apply id='id7'><minus/><ci id='id6'>n</ci></apply><cn id='id8' type='integer'>2</cn></apply><apply id='id14'><ci id='id10'>u</ci><apply id='id13'><plus/><ci id='id11'>n</ci><cn id='id12' type='integer'>2</cn></apply></apply></apply></apply><cn id='id17' type='integer'>0</cn></apply></annotation-xml><annotation encoding='Maple'>-n*u(n)+(-n-2)*u(n+2) = 0</annotation></semantics></math>