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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 264 |
| 2 | 13488 |
| 3 | 278168 |
| 4 | 3237984 |
| 5 | 25290408 |
| 6 | 147204624 |
| 7 | 684347448 |
| 8 | 2666539200 |
| 9 | 9015945800 |
| 10 | 27141718896 |
| 11 | 74182306776 |
| 12 | 186879023392 |
| 13 | 439124493288 |
| 14 | 971672262864 |
| 15 | 2040402823544 |
| 16 | 4092008534400 |
| 17 | 7879085829000 |
| 18 | 14630516376112 |
| 19 | 26297796632856 |
| 20 | 45903762942432 |
[1,264,13488,278168,3237984,25290408,147204624, 684347448,2666539200,9015945800,27141718896, 74182306776,186879023392,439124493288, 971672262864,2040402823544,4092008534400, 7879085829000,14630516376112,26297796632856, 45903762942432] |