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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 69 |
| 5 | 242 |
| 6 | 858 |
| 7 | 3068 |
| 8 | 11050 |
| 9 | 40052 |
| 10 | 145996 |
| 11 | 534888 |
| 12 | 1968685 |
| 13 | 7276050 |
| 14 | 26993490 |
| 15 | 100490220 |
| 16 | 375287550 |
| 17 | 1405622460 |
| 18 | 5278838100 |
| 19 | 19873977240 |
| 20 | 74994427170 |
| 21 | 283595947284 |
| 22 | 1074568266756 |
| 23 | 4079184055640 |
| 24 | 15511924233204 |
| 25 | 59083160374952 |
| 26 | 225384613313944 |
[1,2,6,20,69,242,858,3068,11050,40052,145996, 534888,1968685,7276050,26993490,100490220, 375287550,1405622460,5278838100,19873977240, 74994427170,283595947284,1074568266756, 4079184055640,15511924233204,59083160374952, 225384613313944] |