The fact that most people will pick the number seven when asked to choose a number between one and ten is mentioned by Robert-Houdin in his Secrets of Conjuring And Magic, 1868, in a trick titled “The Thoughts of Two Persons Anticipated”, p. 256. Walter S. Dunkel provided fuller details on succeeding with this force in “Mental Interlude” in The Sphinx, Vol. 5 No. 3, May 1906, p. 34.

Albert Cohn seems the first to have explained in print that 68 is most often thought of when asked to choose a number between fifty and one hundred with both digits even and different, and that 37 is the most frequent choice when thinking of a number between one and fifty with both digits odd and different. His explanation occurs in his routine “Mental Marvels” in Hugard's Magic Monthly, Vol. 3 No. 7, Dec. 1945, p. 171.