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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 3 |
| 3 | 20 |
| 4 | 120 |
| 5 | 763 |
| 6 | 5210 |
| 7 | 38042 |
| 8 | 288616 |
| 9 | 2259818 |
| 10 | 18165437 |
| 11 | 149165130 |
| 12 | 1246782034 |
| 13 | 10576153259 |
| 14 | 90845450184 |
| 15 | 788766653816 |
| 16 | 6912684881941 |
| 17 | 61079444849535 |
| 18 | 543599336199608 |
| 19 | 4869141098476425 |
| 20 | 43865568875289741 |
| 21 | 397232678533509005 |
| 22 | 3614124134441452287 |
[0,3,20,120,763,5210,38042,288616,2259818, 18165437,149165130,1246782034,10576153259, 90845450184,788766653816,6912684881941, 61079444849535,543599336199608,4869141098476425, 43865568875289741,397232678533509005, 3614124134441452287] |