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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 42 |
| 5 | 153 |
| 6 | 595 |
| 7 | 2343 |
| 8 | 9542 |
| 9 | 39413 |
| 10 | 166281 |
| 11 | 708897 |
| 12 | 3061940 |
| 13 | 13353865 |
| 14 | 58750955 |
| 15 | 260487890 |
| 16 | 1162823080 |
| 17 | 5222031742 |
| 18 | 23582500740 |
| 19 | 107010241453 |
| 20 | 487788886128 |
| 21 | 2232519065432 |
| 22 | 10255861643899 |
| 23 | 47276532426065 |
| 24 | 218615273009775 |
| 25 | 1013881795097680 |
| 26 | 4714877471655987 |
| 27 | 21980833198519547 |
[1,1,4,12,42,153,595,2343,9542,39413,166281, 708897,3061940,13353865,58750955,260487890, 1162823080,5222031742,23582500740,107010241453, 487788886128,2232519065432,10255861643899, 47276532426065,218615273009775,1013881795097680, 4714877471655987,21980833198519547] |