Other notable constants and where they show up:

Euler–Mascheroni Constant (integrals and sums involving the harmonic series, Gamma functions)

Catalan’s Constant (certain trigonometric series, lattice Green’s function)

Feigenbaum Constants (logistic map, chaos in dynamical systems)

Khinchin’s Constant (partial quotients in simple continued fractions)

Glaisher–Kinkelin Constant (asymptotic expansions of the Barnes G-function, combinatorial limits and certain product expansions)

Ramanujan’s Constant (complex multiplication of elliptic curves)

Omega Constant (Omega times e to the power of Omega = 1, Lambert W function, x^x^x^... = 2)