f-1(13 + 4) = 2f-1(13) + 1
f-1(17) = 2f-1(13) + 1
f-1(9 + 4) = 2f-1(9) + 1
f-1(13) = 2f-1(9) + 1
f-1(5 + 4) = 2f-1(5) + 1
f-1(9) = 2f-1(5) + 1
f(2) = 5, so f-1(5) = 2
Substitute:
f-1(9) = 2(2) + 1 = 5
f-1(13) = 2(5) + 1 = 11
f-1(17) = 2(11) + 1 = 23
