Makowski, A. "Generalization of Morrow's -Numbers." Simon Stevin36, 71, 1962/1963.Ribenboim,
P. The
New Book of Prime Number Records. New York: Springer-Verlag, pp. 125-126,
1989.Sloane, N. J. A. Sequences A002997/M5462,
A033553, A050990,
A050992, and A050993
in "The On-Line Encyclopedia of Integer Sequences."