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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 15 |
| 4 | 54 |
| 5 | 190 |
| 6 | 660 |
| 7 | 2276 |
| 8 | 7816 |
| 9 | 26776 |
| 10 | 91600 |
| 11 | 313104 |
| 12 | 1069728 |
| 13 | 3653728 |
| 14 | 12477504 |
| 15 | 42606656 |
| 16 | 145479808 |
| 17 | 496722304 |
| 18 | 1695962368 |
| 19 | 5790470400 |
| 20 | 19770087936 |
| 21 | 67499673088 |
| 22 | 230459040768 |
| 23 | 786837865472 |
| 24 | 2686435477504 |
[1,4,15,54,190,660,2276,7816,26776,91600,313104, 1069728,3653728,12477504,42606656,145479808, 496722304,1695962368,5790470400,19770087936, 67499673088,230459040768,786837865472, 2686435477504] |