A curious approximation to the Feigenbaum constant δ is given by π + tan^(-1)(e^π) = 4.6692..., where e^π is Gelfond's constant, which is good to 6 digits to the right of the decimal point. M. Trott noted δ≈2G + 3, where G is Gauss's constant, which is good to 4 decimal digits, and δ≈9/T, where T is the tetranacci constant, which is good to 3 decimal digits.

almost integer | Feigenbaum constant