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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 22 |
| 5 | 145 |
| 6 | 936 |
| 7 | 4459 |
| 8 | 52060 |
| 9 | 376905 |
| 10 | 3039940 |
| 11 | 39240091 |
| 12 | 420688104 |
| 13 | 4175453737 |
| 14 | 49517332242 |
| 15 | 857400548775 |
| 16 | 9885572962696 |
| 17 | 120164315812225 |
| 18 | 2162210359719852 |
| 19 | 36242822778024691 |
| 20 | 542315443367722240 |
| 21 | 7358279105365617681 |
| 22 | 162325807196140641922 |
[1,1,2,9,22,145,936,4459,52060,376905,3039940, 39240091,420688104,4175453737,49517332242, 857400548775,9885572962696,120164315812225, 2162210359719852,36242822778024691, 542315443367722240,7358279105365617681, 162325807196140641922] |