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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 18 |
| 3 | 18 |
| 4 | 55 |
| 5 | 192 |
| 6 | 652 |
| 7 | 2002 |
| 8 | 6741 |
| 9 | 23631 |
| 10 | 79836 |
| 11 | 274822 |
| 12 | 954282 |
| 13 | 3306096 |
| 14 | 11462662 |
| 15 | 39849725 |
| 16 | 138545796 |
| 17 | 481560761 |
| 18 | 1674865229 |
| 19 | 5826326576 |
| 20 | 20267377567 |
| 21 | 70508970351 |
| 22 | 245315398653 |
| 23 | 853512851244 |
| 24 | 2969629901018 |
| 25 | 10332484940737 |
[1,18,18,55,192,652,2002,6741,23631,79836,274822, 954282,3306096,11462662,39849725,138545796, 481560761,1674865229,5826326576,20267377567, 70508970351,245315398653,853512851244, 2969629901018,10332484940737] |