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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 7 |
| 4 | 30 |
| 5 | 146 |
| 6 | 852 |
| 7 | 5823 |
| 8 | 45740 |
| 9 | 405844 |
| 10 | 4012710 |
| 11 | 43733975 |
| 12 | 520795002 |
| 13 | 6726601062 |
| 14 | 93651619880 |
| 15 | 1398047697151 |
| 16 | 22275111534552 |
| 17 | 377278848390248 |
| 18 | 6768744159489930 |
| 19 | 128228860181918439 |
| 20 | 2557808459478878870 |
| 21 | 53585748788874537850 |
| 22 | 1176328664895760953852 |
[0,2,7,30,146,852,5823,45740,405844,4012710, 43733975,520795002,6726601062,93651619880, 1398047697151,22275111534552,377278848390248, 6768744159489930,128228860181918439, 2557808459478878870,53585748788874537850, 1176328664895760953852] |