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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 2 |
| 4 | 26 |
| 5 | 242 |
| 6 | 2090 |
| 7 | 17028 |
| 8 | 135192 |
| 9 | 1052482 |
| 10 | 8090534 |
| 11 | 61600242 |
| 12 | 465672902 |
| 13 | 3500492506 |
| 14 | 26194710582 |
| 15 | 195292190860 |
| 16 | 1451475017832 |
| 17 | 10759514011692 |
| 18 | 79578500716274 |
| 19 | 587419268130996 |
| 20 | 4328676402587912 |
| 21 | 31849540056873120 |
[0,0,2,26,242,2090,17028,135192,1052482,8090534, 61600242,465672902,3500492506,26194710582, 195292190860,1451475017832,10759514011692, 79578500716274,587419268130996,4328676402587912, 31849540056873120] |