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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 12 |
| 3 | 36 |
| 4 | 108 |
| 5 | 324 |
| 6 | 966 |
| 7 | 2880 |
| 8 | 8592 |
| 9 | 25632 |
| 10 | 76464 |
| 11 | 228096 |
| 12 | 680430 |
| 13 | 2029788 |
| 14 | 6055044 |
| 15 | 18062748 |
| 16 | 53882820 |
| 17 | 160737372 |
| 18 | 479494254 |
| 19 | 1430375112 |
| 20 | 4266939480 |
| 21 | 12728669832 |
| 22 | 37970783640 |
| 23 | 113270312520 |
| 24 | 337895678406 |
| 25 | 1007973642420 |
[1,4,12,36,108,324,966,2880,8592,25632,76464, 228096,680430,2029788,6055044,18062748,53882820, 160737372,479494254,1430375112,4266939480, 12728669832,37970783640,113270312520,337895678406, 1007973642420] |