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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 21 |
| 3 | 105 |
| 4 | 535 |
| 5 | 2670 |
| 6 | 12996 |
| 7 | 59546 |
| 8 | 266875 |
| 9 | 1161894 |
| 10 | 4939778 |
| 11 | 20528320 |
| 12 | 83636061 |
| 13 | 334496221 |
| 14 | 1315381029 |
| 15 | 5091782355 |
| 16 | 19424086781 |
| 17 | 73092029218 |
| 18 | 271537720562 |
| 19 | 996656173345 |
| 20 | 3616680935702 |
| 21 | 12983391870459 |
| 22 | 46133749660407 |
| 23 | 162337625047433 |
| 24 | 565962994479384 |
| 25 | 1955721907216420 |
| 26 | 6701061533668542 |
| 27 | 22774651422340672 |
[1,1,21,105,535,2670,12996,59546,266875,1161894, 4939778,20528320,83636061,334496221,1315381029, 5091782355,19424086781,73092029218,271537720562, 996656173345,3616680935702,12983391870459, 46133749660407,162337625047433,565962994479384, 1955721907216420,6701061533668542, 22774651422340672] |