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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 74 |
| 5 | 286 |
| 6 | 1124 |
| 7 | 4460 |
| 8 | 17768 |
| 9 | 70930 |
| 10 | 283440 |
| 11 | 1133200 |
| 12 | 4531686 |
| 13 | 18124522 |
| 14 | 72493652 |
| 15 | 289965744 |
| 16 | 1159845258 |
| 17 | 4639345612 |
| 18 | 18557311624 |
| 19 | 74229104872 |
| 20 | 296916136278 |
| 21 | 1187663978718 |
| 22 | 4750654782144 |
| 23 | 19002616863186 |
| 24 | 76010462922018 |
[2,6,20,74,286,1124,4460,17768,70930,283440, 1133200,4531686,18124522,72493652,289965744, 1159845258,4639345612,18557311624,74229104872, 296916136278,1187663978718,4750654782144, 19002616863186,76010462922018] |