| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 13 |
| 4 | 66 |
| 5 | 365 |
| 6 | 2132 |
| 7 | 12940 |
| 8 | 80804 |
| 9 | 515776 |
| 10 | 3350165 |
| 11 | 22071930 |
| 12 | 147141469 |
| 13 | 990714900 |
| 14 | 6727506071 |
| 15 | 46020535285 |
| 16 | 316837676938 |
| 17 | 2193700600205 |
| 18 | 15265011340106 |
| 19 | 106699930507346 |
| 20 | 748827090415380 |
| 21 | 5274495878205514 |
[1,1,3,13,66,365,2132,12940,80804,515776,3350165, 22071930,147141469,990714900,6727506071, 46020535285,316837676938,2193700600205, 15265011340106,106699930507346,748827090415380, 5274495878205514] |