Each banknote is unique at least in having a unique serial number on it.  Certain serial numbers are more interesting, hard to find , and certainly worth collecting.

1. Small numbers : 000003, 000008, 0000033, 0000088, etc

2. Solid numbers : 000001, 333333, 888888, 1000000, etc.

3. Chinese Lucky numbers : 000168, 168168, 000328, 328328, 300000, 800000, 088888, 188888, 288888, 388888, 688888, 788888, 988888, etc. (numbers are specially lucky to Chinese people.)

4.  Numbers of 3 Stripes : 000888, 888000, 111888, 888111, 222888, 888222, 333888, 888333, 666888, 888666, 888999, 999888, etc.

5. Ladders : 012345, 543210, 345678, 876543, etc. (numbers are incremental or decremental in continuous sequence.)

6. Paired Ladders : 112233, 667788, 998877, etc.

7. Repeated numbers : 008008, 800800, 080808, 808080 181818, 383838, 838383, 338338, 668668, etc.

8. RADAR : 080080, 282282, 383383, 388883 , 800008, 822228, 808808, 818818, 828828, 838838, etc. (Where you can read the numbers same from right-to-left as it does from left-to-right.)

9. Same number with Different prefixes : A/000038, AA/000038, B/000038, C/000038, D/000038, E/000038, F/000038, etc.

10. Twins (Same number with Same prefixes) : ZZ000777 ($50) & ZZ000777 ($1,000), AA328328 ($100) & AA328328 ($500), DN 000068 (Year 1999 $100) & DN 000068 (Year 2003 $100), etc.

11. Special events : Some collect banknotes with numbers 001952 if they were born in 1952 or with 000214, 001997, 002000,  if they have a certain event in 214, 1997, 2000. This is more of a personal type of special-numbered note.

12. Combined numbers : 008808, 088000, 088880, 808888, 880888, 888088, 888808, 303333, 333303, 888828, 888880, etc. (The numbers are combination of only 2 or 3 numbers.)

13. Rotator numbers : 066990, 069690, 068890, 089680, 988886 etc. (The numbers are being read the same rotating upside down. They contain only the numbers 0, 6, 8 and 9.  Rotators which have only 0's and 8's are also radar, e.g. 080080, 008800, 088880, 800008, 808808, 880088, etc.  For notes with arabic numbers, they must contain only 0, 5, 7 and 8 and thus 755558 (VOOOO^) is a rotator.)