In the following sequence of numbers, each term, starting with the third, is obtained by adding three times the previous term plus twice the previous term to the previous one: $$a_1, a_2, 78, a_4, a_5, 3438, a_7, a_8,…$$As seen in the sequence, the third term is $78$ and the sixth term is $3438$. What is the value of the term $a_7$?