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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 16 |
| 4 | 74 |
| 5 | 366 |
| 6 | 1900 |
| 7 | 10210 |
| 8 | 56315 |
| 9 | 317005 |
| 10 | 1813860 |
| 11 | 10518652 |
| 12 | 61684208 |
| 13 | 365177622 |
| 14 | 2179549853 |
| 15 | 13100686947 |
| 16 | 79232836206 |
| 17 | 481821573994 |
| 18 | 2944253855746 |
| 19 | 18069720545174 |
| 20 | 111333779015326 |
| 21 | 688399685561554 |
| 22 | 4270250156814421 |
| 23 | 26567075153764929 |
[1,1,4,16,74,366,1900,10210,56315,317005,1813860, 10518652,61684208,365177622,2179549853, 13100686947,79232836206,481821573994, 2944253855746,18069720545174,111333779015326, 688399685561554,4270250156814421, 26567075153764929] |