The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 3 |
| 4 | 12 |
| 5 | 30 |
| 6 | 89 |
| 7 | 248 |
| 8 | 706 |
| 9 | 1995 |
| 10 | 5652 |
| 11 | 15998 |
| 12 | 45297 |
| 13 | 128240 |
| 14 | 363074 |
| 15 | 1027923 |
| 16 | 2910236 |
| 17 | 8239390 |
| 18 | 23327177 |
| 19 | 66043368 |
| 20 | 186980482 |
| 21 | 529374875 |
| 22 | 1498754084 |
| 23 | 4243238398 |
| 24 | 12013359841 |
| 25 | 34011950560 |
| 26 | 96293859202 |
| 27 | 272624979363 |
[0,2,3,12,30,89,248,706,1995,5652,15998,45297, 128240,363074,1027923,2910236,8239390,23327177, 66043368,186980482,529374875,1498754084, 4243238398,12013359841,34011950560,96293859202, 272624979363] |