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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 14 |
| 4 | 40 |
| 5 | 298 |
| 6 | 1546 |
| 7 | 8704 |
| 8 | 50450 |
| 9 | 286426 |
| 10 | 1650968 |
| 11 | 9481842 |
| 12 | 54537066 |
| 13 | 313793424 |
| 14 | 1805343618 |
| 15 | 10388621898 |
| 16 | 59779183384 |
| 17 | 343996534162 |
| 18 | 1979528849242 |
| 19 | 11391230879008 |
| 20 | 65551238025090 |
| 21 | 377217128316090 |
| 22 | 2170711959147608 |
[0,2,14,40,298,1546,8704,50450,286426,1650968, 9481842,54537066,313793424,1805343618,10388621898, 59779183384,343996534162,1979528849242, 11391230879008,65551238025090,377217128316090, 2170711959147608] |