| n | a(n) |
|---|---|
| 0 | 4 |
| 1 | 8 |
| 2 | 20 |
| 3 | 56 |
| 4 | 164 |
| 5 | 488 |
| 6 | 1460 |
| 7 | 4376 |
| 8 | 13124 |
| 9 | 39368 |
| 10 | 118100 |
| 11 | 354296 |
| 12 | 1062884 |
| 13 | 3188648 |
| 14 | 9565940 |
| 15 | 28697816 |
| 16 | 86093444 |
| 17 | 258280328 |
| 18 | 774840980 |
| 19 | 2324522936 |
| 20 | 6973568804 |
| 21 | 20920706408 |
| 22 | 62762119220 |
| 23 | 188286357656 |
| 24 | 564859072964 |
| 25 | 1694577218888 |
| 26 | 5083731656660 |
| 27 | 15251194969976 |
[4,8,20,56,164,488,1460,4376,13124,39368,118100, 354296,1062884,3188648,9565940,28697816,86093444, 258280328,774840980,2324522936,6973568804, 20920706408,62762119220,188286357656,564859072964, 1694577218888,5083731656660,15251194969976] |