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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 12 |
| 3 | 36 |
| 4 | 96 |
| 5 | 248 |
| 6 | 624 |
| 7 | 1548 |
| 8 | 3804 |
| 9 | 9292 |
| 10 | 22608 |
| 11 | 54864 |
| 12 | 132912 |
| 13 | 321620 |
| 14 | 777660 |
| 15 | 1879380 |
| 16 | 4540368 |
| 17 | 10966504 |
| 18 | 26483712 |
| 19 | 63950652 |
| 20 | 154412076 |
| 21 | 372818588 |
| 22 | 900120096 |
| 23 | 2173173408 |
| 24 | 5246652384 |
| 25 | 12666778276 |
| 26 | 30580694508 |
| 27 | 73828952964 |
| 28 | 178239871680 |
| 29 | 430310753240 |
| 30 | 1038864706320 |
| 31 | 2508045550956 |
[1,4,12,36,96,248,624,1548,3804,9292,22608,54864, 132912,321620,777660,1879380,4540368,10966504, 26483712,63950652,154412076,372818588,900120096, 2173173408,5246652384,12666778276,30580694508, 73828952964,178239871680,430310753240, 1038864706320,2508045550956] |