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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 24 |
| 3 | 90 |
| 4 | 318 |
| 5 | 1098 |
| 6 | 3696 |
| 7 | 12270 |
| 8 | 40224 |
| 9 | 130650 |
| 10 | 421176 |
| 11 | 1348998 |
| 12 | 4299018 |
| 13 | 13635630 |
| 14 | 43092888 |
| 15 | 135698970 |
| 16 | 426144654 |
| 17 | 1334488074 |
| 18 | 4170038328 |
| 19 | 13001153910 |
| 20 | 40464412482 |
| 21 | 125706293478 |
| 22 | 389962873920 |
| 23 | 1207855307874 |
| 24 | 3736709089176 |
| 25 | 11544946664622 |
| 26 | 35633199126576 |
[1,6,24,90,318,1098,3696,12270,40224,130650, 421176,1348998,4299018,13635630,43092888, 135698970,426144654,1334488074,4170038328, 13001153910,40464412482,125706293478,389962873920, 1207855307874,3736709089176,11544946664622, 35633199126576] |