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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 15 |
| 3 | 91 |
| 4 | 613 |
| 5 | 4410 |
| 6 | 33190 |
| 7 | 258129 |
| 8 | 2058281 |
| 9 | 16737259 |
| 10 | 138268611 |
| 11 | 1157197639 |
| 12 | 9790774861 |
| 13 | 83606543660 |
| 14 | 719638883748 |
| 15 | 6237175439640 |
| 16 | 54386540912490 |
| 17 | 476782443732437 |
| 18 | 4199713449255749 |
| 19 | 37151346765537606 |
| 20 | 329914740292813170 |
| 21 | 2939975733035070000 |
[1,3,15,91,613,4410,33190,258129,2058281,16737259, 138268611,1157197639,9790774861,83606543660, 719638883748,6237175439640,54386540912490, 476782443732437,4199713449255749, 37151346765537606,329914740292813170, 2939975733035070000] |