what is the sequence

Question

if the third number is 108 and the sixth number is 23238 what is the number of the first sequence?

Answer 1

If the sixth number is 23328, then we have;

a₁=3

a_n=6∗a_n-1

so,

a₁=3

a₂=18

a₃=108

a₄=648

a₅=3888

a₆=23328