The sum of the reciprocals of those positive integers whose decimal expansion contains no '9'. Kempner (1914) proved the series converges (despite the harmonic series diverging). Canonical numeric value corresponds to digit 9.
The sum of the reciprocals of those positive integers whose decimal expansion contains no '9'. Kempner (1914) proved the series converges (despite the harmonic series diverging). Canonical numeric value corresponds to digit 9.