series complete it- 3,4,7,8,15,16,31,32,63,?,?

Question

please complete my question quickly

 

Answer 1

^a₁ = 3

a₂ = 4

 

thereafter, if n > 2 and is odd, a_n = 2a_n-1 - 1;

and if n>3 and is even, a_n = 2a_n-2