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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 3 |
| 3 | 12 |
| 4 | 21 |
| 5 | 77 |
| 6 | 168 |
| 7 | 609 |
| 8 | 987 |
| 9 | 3572 |
| 10 | 7755 |
| 11 | 28059 |
| 12 | 47376 |
| 13 | 171409 |
| 14 | 372099 |
| 15 | 1346268 |
| 16 | 2178309 |
| 17 | 7881197 |
| 18 | 17108664 |
| 19 | 61899729 |
| 20 | 104512485 |
| 21 | 378129724 |
| 22 | 820851717 |
| 23 | 2969869413 |
| 24 | 4809706272 |
| 25 | 17401680769 |
| 26 | 37775923491 |
| 27 | 136674575148 |
[0,1,3,12,21,77,168,609,987,3572,7755,28059,47376, 171409,372099,1346268,2178309,7881197,17108664, 61899729,104512485,378129724,820851717,2969869413, 4809706272,17401680769,37775923491,136674575148] |