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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 21 |
| 4 | 112 |
| 5 | 570 |
| 6 | 2772 |
| 7 | 13013 |
| 8 | 59488 |
| 9 | 266526 |
| 10 | 1175720 |
| 11 | 5123426 |
| 12 | 22108704 |
| 13 | 94645460 |
| 14 | 402503220 |
| 15 | 1702300725 |
| 16 | 7165821120 |
| 17 | 30043474230 |
| 18 | 125523450360 |
| 19 | 522857438070 |
| 20 | 2172127120800 |
| 21 | 9002522512620 |
| 22 | 37233403401480 |
| 23 | 153704429299746 |
| 24 | 633442159732032 |
| 25 | 2606543487445100 |
| 26 | 10710790748646352 |
| 27 | 43957192722175908 |
[0,1,4,21,112,570,2772,13013,59488,266526,1175720, 5123426,22108704,94645460,402503220,1702300725, 7165821120,30043474230,125523450360,522857438070, 2172127120800,9002522512620,37233403401480, 153704429299746,633442159732032,2606543487445100, 10710790748646352,43957192722175908] |