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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 6 |
| 3 | 42 |
| 4 | 416 |
| 5 | 5210 |
| 6 | 79212 |
| 7 | 1417094 |
| 8 | 29168624 |
| 9 | 679100562 |
| 10 | 17645739500 |
| 11 | 506235093782 |
| 12 | 15893604725352 |
| 13 | 542039221415354 |
| 14 | 19954673671286564 |
| 15 | 788708093950072830 |
| 16 | 33312472504166976992 |
| 17 | 1497371019734704549538 |
| 18 | 71368260385615670087388 |
| 19 | 3595248209512068272420582 |
| 20 | 190872048208819769608101080 |
[1,1,6,42,416,5210,79212,1417094,29168624, 679100562,17645739500,506235093782,15893604725352, 542039221415354,19954673671286564, 788708093950072830,33312472504166976992, 1497371019734704549538,71368260385615670087388, 3595248209512068272420582, 190872048208819769608101080] |