A strange series!

Since the terms are made by power of $3$ or sum of powers of $3$ ,

if we convert this terms into trinary ( base $3$ ) we will find just binary codes(only made of $1$ 's and $0$ 's.)

Now the question is "what is the $100^{th}$ binary number?". And it is very simple. Just have to convert $100$ into binary. And it is $\ \ 1100100$ . Now we can say that $1100100$ is base $3$ representation of the $100^{th}$ term of the strange series. Now just have to convert $1100100$ from base $3$ to decimal.

Therefore the $100^{th}$ term is $1\times3^6+1\times3^5+0\times3^4+0\times3^3+1\times3^2+0\times3^1+0\times3^0= \fbox{981}$