In the following number series, one number is wrong. Find that wrong number. 9, 17, 34, 65, 129, 257

The series is 9, 17, 34, 65, 129, 257. Pattern: each term is ×2-1, starting from next term: 9×2-1=17, 17×2-0=34 (should be 17×2-1=33), 34×2-3=65, 65×2-1=129, 129×2-1=257. Wait - better pattern: 9×2-1=17, 17×2=34 (but should be 33), 34×2-3=65, 65×2-1=129, 129×2-1=257. The pattern is mostly ×2-1, but 17×2=34 breaks it (should be 33). Actually pattern: differences are 8, 17, 31, 64, 128 - doubling 8, 16, 32, 64, 128. So 9+8=17, 17+16=33 (not 34), 33+32=65, 65+64=129, 129+128=257. So 34 is wrong, should be 33.