The 3x+1 function T(x) takes the values (3x+1)/2 if x is odd and x/2 i
f x is even. Let a be any integer with a not equal 0 (mod 3). If n(k)(
a) counts the number of n with T-(k)(n) = a, then for all sufficiently
large k, (1.302)(k) less than or equal to n(k)(a) less than or equal
to (1.359)(k). If pi(a)(x) counts the number of n with \n\ less than o
r equal to x which eventually reach a under iteration by T, then for s
ufficiently large x, pi(a)(x) greater than or equal to x(.65). The pro
ofs are computer-intensive.