represents an inverse gamma distribution.
InverseGammaDistribution[α, β]
InverseGammaDistribution[α, β, γ, μ]
InverseGammaDistribution[2, 3]
→ InverseGammaDistribution[2, 3]Mean[InverseGammaDistribution[a, b]]
→ Piecewise[{{b/(-1 + a), a > 1}}, Indeterminate]Mean[InverseGammaDistribution[3, 2]]
→ 1Median[InverseGammaDistribution[a, b]]
→ b/InverseGammaRegularized[a, 1/2]