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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 12 |
| 3 | 36 |
| 4 | 108 |
| 5 | 324 |
| 6 | 972 |
| 7 | 2910 |
| 8 | 8712 |
| 9 | 26088 |
| 10 | 78120 |
| 11 | 233928 |
| 12 | 700488 |
| 13 | 2097576 |
| 14 | 6281094 |
| 15 | 18808452 |
| 16 | 56321052 |
| 17 | 168650820 |
| 18 | 505017180 |
| 19 | 1512250884 |
| 20 | 4528366236 |
| 21 | 13559985966 |
| 22 | 40604758920 |
| 23 | 121589096856 |
| 24 | 364092999624 |
| 25 | 1090259865432 |
[1,4,12,36,108,324,972,2910,8712,26088,78120, 233928,700488,2097576,6281094,18808452,56321052, 168650820,505017180,1512250884,4528366236, 13559985966,40604758920,121589096856,364092999624, 1090259865432] |