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| n | a(n) |
|---|---|
| 1 | 3 |
| 2 | 21 |
| 3 | 120 |
| 4 | 525 |
| 5 | 2268 |
| 6 | 12936 |
| 7 | 41184 |
| 8 | 199485 |
| 9 | 948090 |
| 10 | 3879876 |
| 11 | 12697776 |
| 12 | 81124680 |
| 13 | 218412600 |
| 14 | 1123264800 |
| 15 | 5584230720 |
| 16 | 18934032285 |
| 17 | 63007367940 |
| 18 | 412918656150 |
| 19 | 1060357914000 |
| 20 | 6203093796900 |
| 21 | 25836377973120 |
| 22 | 88372156476240 |
| 23 | 296403506193600 |
| 24 | 1999351428352200 |
| 25 | 5878093199355468 |
| 26 | 24300008114457096 |
| 27 | 116816365538886720 |
| 28 | 458921436045626400 |
| 29 | 1353026992479346800 |
[3,21,120,525,2268,12936,41184,199485,948090, 3879876,12697776,81124680,218412600,1123264800, 5584230720,18934032285,63007367940,412918656150, 1060357914000,6203093796900,25836377973120, 88372156476240,296403506193600,1999351428352200, 5878093199355468,24300008114457096, 116816365538886720,458921436045626400, 1353026992479346800] |