| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 13 |
| 4 | 51 |
| 5 | 183 |
| 6 | 771 |
| 7 | 3087 |
| 8 | 13601 |
| 9 | 59933 |
| 10 | 278797 |
| 11 | 1311719 |
| 12 | 6453606 |
| 13 | 32179898 |
| 14 | 166075956 |
| 15 | 871713213 |
| 16 | 4704669005 |
| 17 | 25831172649 |
| 18 | 145260890323 |
[1,4,13,51,183,771,3087,13601,59933,278797, 1311719,6453606,32179898,166075956,871713213, 4704669005,25831172649,145260890323] |