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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 13 |
| 4 | 37 |
| 5 | 130 |
| 6 | 427 |
| 7 | 1441 |
| 8 | 4954 |
| 9 | 16987 |
| 10 | 58843 |
| 11 | 204610 |
| 12 | 713893 |
| 13 | 2500183 |
| 14 | 8778478 |
| 15 | 30898309 |
| 16 | 108987427 |
| 17 | 385136680 |
| 18 | 1363252603 |
| 19 | 4832572951 |
| 20 | 17153677534 |
| 21 | 60961916965 |
| 22 | 216887253409 |
| 23 | 772400234074 |
| 24 | 2753261490919 |
| 25 | 9822393082513 |
[1,1,4,13,37,130,427,1441,4954,16987,58843,204610, 713893,2500183,8778478,30898309,108987427, 385136680,1363252603,4832572951,17153677534, 60961916965,216887253409,772400234074, 2753261490919,9822393082513] |