The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 81 |
| 2 | 306 |
| 3 | 1276 |
| 4 | 4672 |
| 5 | 18784 |
| 6 | 70688 |
| 7 | 278352 |
| 8 | 1062192 |
| 9 | 4143280 |
| 10 | 15915216 |
| 11 | 61792048 |
| 12 | 238127760 |
| 13 | 922461744 |
| 14 | 3560485008 |
| 15 | 13777495472 |
| 16 | 53218656784 |
| 17 | 205822482224 |
| 18 | 795331807888 |
| 19 | 3075135853232 |
| 20 | 11884984533264 |
| 21 | 45947260928560 |
[81,306,1276,4672,18784,70688,278352,1062192, 4143280,15915216,61792048,238127760,922461744, 3560485008,13777495472,53218656784,205822482224, 795331807888,3075135853232,11884984533264, 45947260928560] |