<math xmlns='http://www.w3.org/1998/Math/MathML'><semantics><mrow xref='id14'><mrow xref='id3'><mi xref='id1'>u</mi><mo>⁡</mo><mfenced><mi xref='id2'>n</mi></mfenced></mrow><mo>=</mo><mrow xref='id13'><mo>-</mo><mrow xref='id12'><mfrac><mrow xref='id6'><msup><mfenced><mn xref='id4'>-1</mn></mfenced><mi xref='id5'>n</mi></msup></mrow><mrow xref='id11'><msup><mfenced><mrow xref='id9'><mi xref='id7'>n</mi><mo>+</mo><mn xref='id8'>1</mn></mrow></mfenced><mn xref='id10'>2</mn></msup></mrow></mfrac></mrow></mrow></mrow><annotation-xml encoding='MathML-Content'><apply id='id14'><eq/><apply id='id3'><ci id='id1'>u</ci><ci id='id2'>n</ci></apply><apply id='id13'><minus/><apply id='id12'><divide/><apply id='id6'><power/><cn id='id4' type='integer'>-1</cn><ci id='id5'>n</ci></apply><apply id='id11'><power/><apply id='id9'><plus/><ci id='id7'>n</ci><cn id='id8' type='integer'>1</cn></apply><cn id='id10' type='integer'>2</cn></apply></apply></apply></apply></annotation-xml><annotation encoding='Maple'>u(n) = -(-1)^n/(n+1)^2</annotation></semantics></math>
