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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 4 |
| 3 | 12 |
| 4 | 51 |
| 5 | 258 |
| 6 | 1553 |
| 7 | 10876 |
| 8 | 87014 |
| 9 | 783133 |
| 10 | 7831333 |
| 11 | 86144666 |
| 12 | 1033736003 |
| 13 | 13438568048 |
| 14 | 188139952678 |
| 15 | 2822099290183 |
| 16 | 45153588642933 |
| 17 | 767611006929867 |
| 18 | 13816998124737613 |
| 19 | 262522964370014656 |
| 20 | 5250459287400293135 |
[2,4,12,51,258,1553,10876,87014,783133,7831333, 86144666,1033736003,13438568048,188139952678, 2822099290183,45153588642933,767611006929867, 13816998124737613,262522964370014656, 5250459287400293135] |