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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 21 |
| 5 | 74 |
| 6 | 247 |
| 7 | 769 |
| 8 | 2247 |
| 9 | 6238 |
| 10 | 16649 |
| 11 | 43132 |
| 12 | 109257 |
| 13 | 272073 |
| 14 | 668704 |
| 15 | 1626916 |
| 16 | 3926643 |
| 17 | 9416939 |
| 18 | 22468173 |
| 19 | 53383884 |
| 20 | 126404204 |
| 21 | 298455204 |
| 22 | 703023125 |
| 23 | 1652724170 |
| 24 | 3878899500 |
| 25 | 9090904341 |
| 26 | 21280894049 |
| 27 | 49766276975 |
| 28 | 116280945813 |
[1,2,6,21,74,247,769,2247,6238,16649,43132,109257, 272073,668704,1626916,3926643,9416939,22468173, 53383884,126404204,298455204,703023125,1652724170, 3878899500,9090904341,21280894049,49766276975, 116280945813] |