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| n | a(n) |
|---|---|
| 4 | 1 |
| 5 | 4 |
| 6 | 15 |
| 7 | 50 |
| 8 | 160 |
| 9 | 496 |
| 10 | 1509 |
| 11 | 4530 |
| 12 | 13475 |
| 13 | 39820 |
| 14 | 117117 |
| 15 | 343278 |
| 16 | 1003665 |
| 17 | 2929200 |
| 18 | 8537910 |
| 19 | 24863724 |
| 20 | 72363951 |
| 21 | 210532540 |
| 22 | 612398025 |
| 23 | 1781252110 |
| 24 | 5181318054 |
| 25 | 15073505216 |
| 26 | 43860668800 |
| 27 | 127657036000 |
| 28 | 371654416575 |
| 29 | 1082359229796 |
[1,4,15,50,160,496,1509,4530,13475,39820,117117, 343278,1003665,2929200,8537910,24863724,72363951, 210532540,612398025,1781252110,5181318054, 15073505216,43860668800,127657036000,371654416575, 1082359229796] |