© The London Mathematical Society 2006
BENFORD'S LAW FOR THE 3x + 1 FUNCTION
Department of Mathematics, The University of Michigan Ann Arbor, MI 48109-1043, USA lagarias{at}umich.edu
Department of Mathematics, Stanford University Stanford, CA 94305-2125, USA ksound{at}math.stanford.edu
Received 14 September 2005. Revision received 10 January 2006.
Benford's law (to base B) for an infinite sequence {xk : k
1} of positive quantities xk is the assertion that {logB xk : k
1} is uniformly distributed (mod 1). The 3x + 1 function T(n) is given by T(n) = (3n + 1)/2 if n is odd, and T(n) = n/2 if n is even. This paper studies the initial iterates xk = T(k)(x0) for 1
k
N of the 3x + 1 function, where N is fixed. It shows that for most initial values x0, such sequences approximately satisfy Benford's law, in the sense that the discrepancy of the finite sequence {logB xk : 1
k
N} is small.