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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 4 |
| 5 | 9 |
| 6 | 20 |
| 7 | 47 |
| 8 | 111 |
| 9 | 270 |
| 10 | 664 |
| 11 | 1659 |
| 12 | 4184 |
| 13 | 10662 |
| 14 | 27367 |
| 15 | 70747 |
| 16 | 183925 |
| 17 | 480656 |
| 18 | 1261630 |
| 19 | 3324772 |
| 20 | 8792592 |
| 21 | 23327249 |
| 22 | 62067785 |
| 23 | 165586565 |
[1,1,2,4,9,20,47,111,270,664,1659,4184,10662, 27367,70747,183925,480656,1261630,3324772,8792592, 23327249,62067785,165586565] |