ಕಾಣೆಯಾಗಿರುವ ಅಕ್ಷರವನ್ನು ಸೇರಿಸಿ?

Going clockwise: 3, 5, 8, 13, 22, ?. The differences 2, 3, 5, 9 follow 'double the previous difference and subtract 1', so the next difference is 17 and ? = 22 + 17 = 39.