Question

write a recursive formula for sequence: 15, 26, 48, 92, 180. I know the sequence is multiply difference of 2 numbers by 2 and add next number but don't know how to put in formula.

Answer 1

i notice that to get to the next term we add 4 less the previous term to the previous term

Answer 2

since the difference is 11,22,44,88
hence
next term=previuos term +4 less previuos term
\[a_{n+1}=a_n+a_n-4=2a_n-4\]