Question

What is the rule pattern for 9,11,15,23,39,7?

Answer 1

Add 2 then multiply by 2

Answer 2

$9,11,15,23,39,71 \\9+2\rightarrow11+4\rightarrow15+8\rightarrow23+16\rightarrow39+32=71 \\9+2^1\rightarrow11+2^2\rightarrow15+2^3\rightarrow23+2^4\rightarrow39+2^5\rightarrow71 \\ \\a_n=7+2^n$