Figure out the pattern

Define a Fibonacci-like sequence $\{G_n\}_{n \in \mathbb N}$ as follows. $G_0 =0$ , $G_1 = 1$ , $G_2 = 1$ , and $G_n = G_{n-1}+G_{n-2}+G_{n-3}$ . Then the first few values of $G_n$ are:

$\begin{array} {cccc} G_0 = 0 & G_1 = 1 & G_2 = 1 & \underbrace{G_3 = 2}_{0+1+1} \\ \underbrace{G_4 = 4}_{1+1+2} & \underbrace{G_5 = 7}_{1+2+4} & \underbrace{G_6 = 13}_{2+4+7} & \underbrace{G_6 = 24}_{4+7+13} \\ \underbrace{G_7 = 44}_{7+13+24} & \underbrace{G_8 = \boxed{81}}_{13+24+44} & \cdots \end{array}$

The sequence is a generalization of Fibonacci numbers. Each term is the total of the previous three numbers. Therefore the result is 13+24+44=81.