Answer
$0,3,12,147,21,612$ and $467,078,547$.
Work Step by Step
${{a}_{n+1}}={{\left( {{a}_{n}} \right)}^{2}}+3$
${{a}_{1}}=0$
$\begin{align}
& {{a}_{n+1}}={{\left( {{a}_{n}} \right)}^{2}}+3 \\
& {{a}_{1+1}}={{\left( {{a}_{1}} \right)}^{2}}+3 \\
& {{a}_{2}}={{0}^{2}}+3 \\
& =3
\end{align}$
$\begin{align}
& {{a}_{n+1}}={{\left( {{a}_{n}} \right)}^{2}}+3 \\
& {{a}_{2+1}}={{\left( {{a}_{2}} \right)}^{2}}+3 \\
& {{a}_{3}}={{3}^{2}}+3 \\
& =12
\end{align}$
$\begin{align}
& {{a}_{n+1}}={{\left( {{a}_{n}} \right)}^{2}}+3 \\
& {{a}_{3+1}}={{\left( {{a}_{3}} \right)}^{2}}+3 \\
& {{a}_{4}}={{\left( 12 \right)}^{2}}+3 \\
& =147
\end{align}$
$\begin{align}
& {{a}_{n+1}}={{\left( {{a}_{n}} \right)}^{2}}+3 \\
& {{a}_{4+1}}={{\left( {{a}_{4}} \right)}^{2}}+3 \\
& {{a}_{5}}={{\left( 144 \right)}^{2}}+3 \\
& =21,612
\end{align}$
$\begin{align}
& {{a}_{n+1}}={{\left( {{a}_{n}} \right)}^{2}}+3 \\
& {{a}_{5+1}}={{\left( {{a}_{5}} \right)}^{2}}+3 \\
& {{a}_{6}}={{\left( 21,612 \right)}^{2}}+3 \\
& =467,078,547
\end{align}$
Thus,
$\begin{align}
& {{a}_{1}}=0 \\
& {{a}_{2}}=3 \\
& {{a}_{3}}=12 \\
\end{align}$
And,
$\begin{align}
& {{a}_{4}}=147 \\
& {{a}_{5}}=21,612 \\
& {{a}_{6}}=467,078,547 \\
\end{align}$
The first six terms are:
$0,3,12,147,21,612$ and $467,078,547$.