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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 18 |
| 3 | 180 |
| 4 | 2028 |
| 5 | 8820 |
| 6 | 34848 |
| 7 | 108288 |
| 8 | 191748 |
| 9 | 720900 |
| 10 | 875520 |
| 11 | 960498 |
| 12 | 990000 |
| 13 | 1355310 |
| 14 | 1629108 |
| 15 | 1713600 |
| 16 | 1756920 |
| 17 | 2334948 |
| 18 | 2609028 |
| 19 | 7376850 |
| 20 | 8448048 |
| 21 | 21639798 |
| 22 | 37148148 |
| 23 | 42023088 |
| 24 | 48893940 |
| 25 | 60544008 |
| 26 | 63840000 |
| 27 | 100328400 |
[4,18,180,2028,8820,34848,108288,191748,720900, 875520,960498,990000,1355310,1629108,1713600, 1756920,2334948,2609028,7376850,8448048,21639798, 37148148,42023088,48893940,60544008,63840000, 100328400] |