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| n | a(n) |
|---|---|
| 0 | 4 |
| 1 | 15 |
| 2 | 52 |
| 3 | 172 |
| 4 | 552 |
| 5 | 1736 |
| 6 | 5384 |
| 7 | 16536 |
| 8 | 50440 |
| 9 | 153112 |
| 10 | 463176 |
| 11 | 1397720 |
| 12 | 4210568 |
| 13 | 12668568 |
| 14 | 38083528 |
| 15 | 114414424 |
| 16 | 343587336 |
| 17 | 1031482904 |
| 18 | 3095956040 |
| 19 | 9291013848 |
| 20 | 27879595144 |
| 21 | 83652416920 |
| 22 | 250985562312 |
| 23 | 753015407192 |
| 24 | 2259167856392 |
| 25 | 6777755227416 |
| 26 | 20333785775944 |
[4,15,52,172,552,1736,5384,16536,50440,153112, 463176,1397720,4210568,12668568,38083528, 114414424,343587336,1031482904,3095956040, 9291013848,27879595144,83652416920,250985562312, 753015407192,2259167856392,6777755227416, 20333785775944] |