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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 21 |
| 3 | 104 |
| 4 | 521 |
| 5 | 2604 |
| 6 | 13021 |
| 7 | 65104 |
| 8 | 325521 |
| 9 | 1627604 |
| 10 | 8138021 |
| 11 | 40690104 |
| 12 | 203450521 |
| 13 | 1017252604 |
| 14 | 5086263021 |
| 15 | 25431315104 |
| 16 | 127156575521 |
| 17 | 635782877604 |
| 18 | 3178914388021 |
| 19 | 15894571940104 |
| 20 | 79472859700521 |
| 21 | 397364298502604 |
| 22 | 1986821492513021 |
| 23 | 9934107462565104 |
[1,4,21,104,521,2604,13021,65104,325521,1627604, 8138021,40690104,203450521,1017252604,5086263021, 25431315104,127156575521,635782877604, 3178914388021,15894571940104,79472859700521, 397364298502604,1986821492513021,9934107462565104] |