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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 21 |
| 3 | 66 |
| 4 | 201 |
| 5 | 606 |
| 6 | 1821 |
| 7 | 5466 |
| 8 | 16401 |
| 9 | 49206 |
| 10 | 147621 |
| 11 | 442866 |
| 12 | 1328601 |
| 13 | 3985806 |
| 14 | 11957421 |
| 15 | 35872266 |
| 16 | 107616801 |
| 17 | 322850406 |
| 18 | 968551221 |
| 19 | 2905653666 |
| 20 | 8716961001 |
| 21 | 26150883006 |
| 22 | 78452649021 |
| 23 | 235357947066 |
| 24 | 706073841201 |
| 25 | 2118221523606 |
[1,6,21,66,201,606,1821,5466,16401,49206,147621, 442866,1328601,3985806,11957421,35872266, 107616801,322850406,968551221,2905653666, 8716961001,26150883006,78452649021,235357947066, 706073841201,2118221523606] |