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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 17 |
| 5 | 47 |
| 6 | 128 |
| 7 | 349 |
| 8 | 948 |
| 9 | 2579 |
| 10 | 7011 |
| 11 | 19058 |
| 12 | 51806 |
| 13 | 140824 |
| 14 | 382800 |
| 15 | 1040560 |
| 16 | 2828536 |
| 17 | 7688760 |
| 18 | 20900217 |
| 19 | 56812680 |
| 20 | 154432878 |
| 21 | 419792086 |
| 22 | 1141113200 |
| 23 | 3101867275 |
| 24 | 8431749450 |
| 25 | 22919871312 |
| 26 | 62302669700 |
| 27 | 169356214910 |
| 28 | 460357921527 |
[0,0,2,6,17,47,128,349,948,2579,7011,19058,51806, 140824,382800,1040560,2828536,7688760,20900217, 56812680,154432878,419792086,1141113200, 3101867275,8431749450,22919871312,62302669700, 169356214910,460357921527] |