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| n | a(n) |
|---|---|
| 0 | 2 |
| 1 | 3 |
| 2 | 6 |
| 3 | 14 |
| 4 | 40 |
| 5 | 152 |
| 6 | 784 |
| 7 | 5168 |
| 8 | 40576 |
| 9 | 363392 |
| 10 | 3629824 |
| 11 | 39918848 |
| 12 | 479005696 |
| 13 | 6227028992 |
| 14 | 87178307584 |
| 15 | 1307674400768 |
| 16 | 20922789953536 |
| 17 | 355687428227072 |
| 18 | 6402373705990144 |
| 19 | 121645100409356288 |
| 20 | 2432902008177688576 |
[2,3,6,14,40,152,784,5168,40576,363392,3629824, 39918848,479005696,6227028992,87178307584, 1307674400768,20922789953536,355687428227072, 6402373705990144,121645100409356288, 2432902008177688576] |