B2⁢n=(-1)n+1⁢4⁢n1-21-2⁢n⁢∫0∞t2⁢n-1ⅇ2⁢π⁢t+1⁢ⅆ⁡t=(-1)n+1⁢2⁢n1-21-2⁢n⁢∫0∞t2⁢n-1⁢ⅇ-π⁢t⁢sech⁡(π⁢t)⁢ⅆ⁡t,