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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 15 |
| 3 | 36 |
| 4 | 93 |
| 5 | 258 |
| 6 | 747 |
| 7 | 2208 |
| 8 | 6585 |
| 9 | 19710 |
| 10 | 59079 |
| 11 | 177180 |
| 12 | 531477 |
| 13 | 1594362 |
| 14 | 4783011 |
| 15 | 14348952 |
| 16 | 43046769 |
| 17 | 129140214 |
| 18 | 387420543 |
| 19 | 1162261524 |
| 20 | 3486784461 |
| 21 | 10460353266 |
| 22 | 31381059675 |
| 23 | 94143178896 |
| 24 | 282429536553 |
| 25 | 847288609518 |
| 26 | 2541865828407 |
| 27 | 7625597485068 |
| 28 | 22876792455045 |
[1,6,15,36,93,258,747,2208,6585,19710,59079, 177180,531477,1594362,4783011,14348952,43046769, 129140214,387420543,1162261524,3486784461, 10460353266,31381059675,94143178896,282429536553, 847288609518,2541865828407,7625597485068, 22876792455045] |