A046253 - OEIS

J. S. Madachy, "Madachy's Mathematical Recreations", Dover N.Y., pp. 163-175.

C. A. Pickover, "Keys to Infinity", Wiley 1995, Ch. 22, pp. 169-171.

David Wells, "Curious and Interesting Numbers", Penguin 1988, pp. 169, 190.