An identity communicated to Feynman as a child by a boy named Morrie Jacobs (Gleick 1992, p. 47). Feynman remembered this fact all his life and referred to it in a letter to Jacobs in 1987 (Gleick 1992, p. 450). It is a special case of the general identity
Anderson, E. C. "Morrie's Law and Experimental Mathematics." J. Recr. Math.29, 85-88, 1998.Beyer,
W. A.; Louck, J. D.; Zeilberger, D. "A Generalization of a Curiosity
that Feynman Remembered All His Life." Math. Mag.69, 43-44, 1996.Gleick,
J. Genius:
The Life and Science of Richard Feynman. New York: Pantheon Books, pp. 47
and 450, 1992.
and 
(Beyer et al. 1996).
