| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 6 |
| 3 | 21 |
| 4 | 91 |
| 5 | 336 |
| 6 | 1337 |
| 7 | 5026 |
| 8 | 19193 |
| 9 | 71769 |
| 10 | 268272 |
| 11 | 992676 |
| 12 | 3659116 |
| 13 | 13400426 |
| 14 | 48863017 |
| 15 | 177299790 |
| 16 | 640713627 |
| 17 | 2305930966 |
| 18 | 8268556438 |
| 19 | 29544196129 |
| 20 | 105215495691 |
| 21 | 373523546056 |
| 22 | 1322096328899 |
| 23 | 4666327388034 |
| 24 | 16425341129078 |
| 25 | 57667752483279 |
| 26 | 201967215942032 |
[1,1,6,21,91,336,1337,5026,19193,71769,268272, 992676,3659116,13400426,48863017,177299790, 640713627,2305930966,8268556438,29544196129, 105215495691,373523546056,1322096328899, 4666327388034,16425341129078,57667752483279, 201967215942032] |