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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 28 |
| 3 | 168 |
| 4 | 1030 |
| 5 | 5802 |
| 6 | 31608 |
| 7 | 171100 |
| 8 | 916768 |
| 9 | 4882310 |
| 10 | 25849910 |
| 11 | 136148532 |
| 12 | 713757316 |
| 13 | 3726366076 |
| 14 | 19383636846 |
| 15 | 100497836596 |
| 16 | 519525218302 |
| 17 | 2678590148146 |
| 18 | 13777413523624 |
| 19 | 70710464750916 |
| 20 | 362190825607320 |
[2,28,168,1030,5802,31608,171100,916768,4882310, 25849910,136148532,713757316,3726366076, 19383636846,100497836596,519525218302, 2678590148146,13777413523624,70710464750916, 362190825607320] |