1887 XXII. 434/2 In Germany the ‘Ludolphische Zahl’ is still a common name for the ratio.]
1894 F. Cajori 154 The value of π is therefore often named ‘Ludolph's number’.
1959 at Ceulen Ludolph van... Known for computations of the value of π (Ludolphian, or Ludolph's number).