The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 3 |
| 2 | 18 |
| 3 | 110 |
| 4 | 663 |
| 5 | 3978 |
| 6 | 23870 |
| 7 | 143223 |
| 8 | 859338 |
| 9 | 5156030 |
| 10 | 30936183 |
| 11 | 185617098 |
| 12 | 1113702590 |
| 13 | 6682215543 |
| 14 | 40093293258 |
| 15 | 240559759550 |
| 16 | 1443358557303 |
| 17 | 8660151343818 |
| 18 | 51960908062910 |
| 19 | 311765448377463 |
| 20 | 1870592690264778 |
[3,18,110,663,3978,23870,143223,859338,5156030, 30936183,185617098,1113702590,6682215543, 40093293258,240559759550,1443358557303, 8660151343818,51960908062910,311765448377463, 1870592690264778] |