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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 15 |
| 3 | 54 |
| 4 | 201 |
| 5 | 672 |
| 6 | 2268 |
| 7 | 7266 |
| 8 | 23208 |
| 9 | 72414 |
| 10 | 224652 |
| 11 | 688929 |
| 12 | 2103975 |
| 13 | 6386907 |
| 14 | 19337091 |
| 15 | 58367817 |
| 16 | 175905741 |
| 17 | 529331190 |
| 18 | 1591515297 |
| 19 | 4781575074 |
| 20 | 14359673454 |
| 21 | 43108645230 |
| 22 | 129387584991 |
| 23 | 388283978589 |
| 24 | 1165099808574 |
| 25 | 3495782937135 |
| 26 | 10488322595625 |
[1,3,15,54,201,672,2268,7266,23208,72414,224652, 688929,2103975,6386907,19337091,58367817, 175905741,529331190,1591515297,4781575074, 14359673454,43108645230,129387584991,388283978589, 1165099808574,3495782937135,10488322595625] |