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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 4 |
| 2 | 40 |
| 3 | 364 |
| 4 | 3280 |
| 5 | 29524 |
| 6 | 265720 |
| 7 | 2391484 |
| 8 | 21523360 |
| 9 | 193710244 |
| 10 | 1743392200 |
| 11 | 15690529804 |
| 12 | 141214768240 |
| 13 | 1270932914164 |
| 14 | 11438396227480 |
| 15 | 102945566047324 |
| 16 | 926510094425920 |
| 17 | 8338590849833284 |
| 18 | 75047317648499560 |
| 19 | 675425858836496044 |
[0,4,40,364,3280,29524,265720,2391484,21523360, 193710244,1743392200,15690529804,141214768240, 1270932914164,11438396227480,102945566047324, 926510094425920,8338590849833284, 75047317648499560,675425858836496044] |