| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 69 |
| 5 | 250 |
| 6 | 924 |
| 7 | 3468 |
| 8 | 13194 |
| 9 | 50602 |
| 10 | 195481 |
| 11 | 759303 |
| 12 | 2961868 |
| 13 | 11595975 |
| 14 | 45528334 |
| 15 | 179189562 |
| 16 | 706689736 |
| 17 | 2791766580 |
| 18 | 11045040490 |
| 19 | 43751719084 |
| 20 | 173495907556 |
| 21 | 688634340547 |
| 22 | 2735513747087 |
| 23 | 10874199425535 |
| 24 | 43253925280236 |
| 25 | 172143832114877 |
| 26 | 685437577427508 |
| 27 | 2730427779738255 |
[1,2,6,20,69,250,924,3468,13194,50602,195481, 759303,2961868,11595975,45528334,179189562, 706689736,2791766580,11045040490,43751719084, 173495907556,688634340547,2735513747087, 10874199425535,43253925280236,172143832114877, 685437577427508,2730427779738255] |