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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 20 |
| 6 | 72 |
| 7 | 272 |
| 8 | 1065 |
| 9 | 4282 |
| 10 | 17576 |
| 11 | 73344 |
| 12 | 310226 |
| 13 | 1327036 |
| 14 | 5730948 |
| 15 | 24952776 |
| 16 | 109417672 |
| 17 | 482779032 |
| 18 | 2141832444 |
| 19 | 9548501992 |
| 20 | 42753897498 |
| 21 | 192184437012 |
| 22 | 866963862560 |
| 23 | 3923596330784 |
| 24 | 17809292215406 |
| 25 | 81055344516420 |
[1,1,2,6,20,72,272,1065,4282,17576,73344,310226, 1327036,5730948,24952776,109417672,482779032, 2141832444,9548501992,42753897498,192184437012, 866963862560,3923596330784,17809292215406, 81055344516420] |