This only gives an unlimited but partial set of valid values of x. The only values for which 3x+1=2exp(n) are x(k)=sum(0 to k)2exp(2k).
For example 1, 5, 21, 85, 341, 1365, etc. Look at the differences: 2exp2, 2exp4, 2exp6, 2exp8, 2exp10, etc. A very small subset of the integers (but infinite!).
If you could show that for every x the serie following ends up at a value smaller than x, the conjecture would be proven. All integers up to 100 converge to
1.so if the 101 orbit ends on a number between 1 and 100 it will do. 101 goes to 304, which goes to 152, which goes to 76, so yes, it delivers. 102 goes 307, which goes 922, which goes 411, 1234, 617, 1852, 926, 463, 1390, 695, 2086, 1043, 3130, 1565, 4696, 2348, 1174, 587, 1762, 881, 2644, 1322, 661, 1984, 992, 496, 248, 124, 62, 31, 94, 47, 142, 71, 214, 107, 322, 161, 484, 242, 121, 364, 182, 91, 274, 137, 412, 206, 103, 310, 155, 466, 233, 700, 350, 175, 526, 263, 790, 345, 1036, 518, 259, 778, 389, 1268, 634, 317, 952, 476, 238, 119, 358, 179, 538, 269, 808, 404, 202, 101, heeee, we had that already, so it delivers!
But now the crucial point:
9, 18, 36, 72, 144, 288, 596, 1192, 2384, 4768,.....
and
12, 24, 48, 96, 192, 384, 768, 1536, 3072, 6144...
and
15, 30, 60, 120, 320, 640, 1280, 2560, 5120...,
will never be part of a series running backwards nor forwards, except as starting point (you can check this by looking at the numbers in the row above, and I used this in fact to correct a number I calculated wrongly). So you
always have to check these numbers separately. Which looks like a considerable reduction, but still are infinite numbers....