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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 2 |
| 5 | 10 |
| 6 | 40 |
| 7 | 156 |
| 8 | 546 |
| 9 | 1986 |
| 10 | 6716 |
| 11 | 23742 |
| 12 | 79472 |
| 13 | 277178 |
| 14 | 925588 |
| 15 | 3205896 |
| 16 | 10711486 |
| 17 | 36963722 |
| 18 | 123712788 |
| 19 | 426075994 |
| 20 | 1429030624 |
| 21 | 4916833424 |
| 22 | 16526958144 |
| 23 | 56840484232 |
| 24 | 191466923584 |
| 25 | 658460090994 |
| 26 | 2222507917328 |
| 27 | 7644360501390 |
| 28 | 25850724646008 |
| 29 | 88938175307354 |
[0,0,0,2,10,40,156,546,1986,6716,23742,79472, 277178,925588,3205896,10711486,36963722,123712788, 426075994,1429030624,4916833424,16526958144, 56840484232,191466923584,658460090994, 2222507917328,7644360501390,25850724646008, 88938175307354] |