Divisible by 3? (2)

Number is divisible by 3 if the sum of its elements is divisible by 3, so the 2nd number: 2+1=3 is divisible by 3. Since every next number has one more 1 the next one that is divisible by 3 is the 5th number. Next 8th,11th, 14th,17th and 20th. That's 7 in total.

The sum of the digits of the last number is $2+19$ and it is divisible by 3 so all numbers divisible by 3 will be $2+19$ $2+16$ $2+13$ $2+10$ $2+7$ $2+4$ $2+1$ Hence there are total $7$ possibilities