The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 3 |
| 2 | 28 |
| 3 | 252 |
| 4 | 2271 |
| 5 | 20440 |
| 6 | 183960 |
| 7 | 1655643 |
| 8 | 14900788 |
| 9 | 134107092 |
| 10 | 1206963831 |
| 11 | 10862674480 |
| 12 | 97764070320 |
| 13 | 879876632883 |
| 14 | 7918889695948 |
| 15 | 71270007263532 |
| 16 | 641430065371791 |
| 17 | 5772870588346120 |
| 18 | 51955835295115080 |
| 19 | 467602517656035723 |
| 20 | 4208422658904321508 |
[3,28,252,2271,20440,183960,1655643,14900788, 134107092,1206963831,10862674480,97764070320, 879876632883,7918889695948,71270007263532, 641430065371791,5772870588346120, 51955835295115080,467602517656035723, 4208422658904321508] |