We know that the rule for divisibility by 3 is that the digits of the number must add up to a multiple of 3. So, it's clear that there are no other such two-digit numbers beyond the ones listed in the problem. Every number divisible by 3 between 100 and 99 is in the sequence, so that gets us through the 39th term of the sequence. Using the rule for divisibility by 3 , it is fairly simple to list out the remaining 11 terms of the sequence: 201, 210. 213, 216, 219, 231, 261, 291, 312, 315, 318. Thus, the 50th term is 318.
