Table[\!\( \*SubsuperscriptBox[\(\[Integral]\), \(0\), \(2\ \[Pi]\)]\( SuperscriptBox[\(Sin[x]\), \(n\)] \[DifferentialD]x\)\), {n, 10}]
Table[\!\( \*SubsuperscriptBox[\(\[Integral]\), \(0\), \(2\ \[Pi]\)]\( SuperscriptBox[\(Sin[x]\), \(n\)] \[DifferentialD]x\)\), {n, 10}]; FindSequenceFunction[%, n]
Integrate[Sin[x]^n, {x, 0, 2 \[Pi]}, Assumptions -> n >= 0]