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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 7 |
| 2 | 56 |
| 3 | 252 |
| 4 | 1260 |
| 5 | 4620 |
| 6 | 18480 |
| 7 | 59815 |
| 8 | 206780 |
| 9 | 605934 |
| 10 | 1869840 |
| 11 | 5038572 |
| 12 | 14164920 |
| 13 | 35459424 |
| 14 | 91871208 |
| 15 | 214864650 |
| 16 | 516936420 |
| 17 | 1134183050 |
| 18 | 2546423880 |
| 19 | 5252058812 |
| 20 | 11031780760 |
| 21 | 21406686756 |
| 22 | 42121344720 |
| 23 | 76871042612 |
| 24 | 141627466344 |
| 25 | 242619996500 |
| 26 | 417750499600 |
[1,7,56,252,1260,4620,18480,59815,206780,605934, 1869840,5038572,14164920,35459424,91871208, 214864650,516936420,1134183050,2546423880, 5252058812,11031780760,21406686756,42121344720, 76871042612,141627466344,242619996500, 417750499600] |