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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 51 |
| 4 | 1176 |
| 5 | 40160 |
| 6 | 1852788 |
| 7 | 109746196 |
| 8 | 8076254064 |
| 9 | 720996043500 |
| 10 | 76639917914560 |
| 11 | 9553107629947662 |
| 12 | 1378566504590365848 |
| 13 | 227792196676700222749 |
| 14 | 42692948669436573948412 |
| 15 | 9000830359064469548726190 |
| 16 | 2119119760287990864773870816 |
| 17 | 553573708504386843864377357273 |
| 18 | 159532387646232647024272055366172 |
| 19 | 50459353730921637796726256001307227 |
[1,1,4,51,1176,40160,1852788,109746196,8076254064, 720996043500,76639917914560,9553107629947662, 1378566504590365848,227792196676700222749, 42692948669436573948412,9000830359064469548726190, 2119119760287990864773870816, 553573708504386843864377357273, 159532387646232647024272055366172, 50459353730921637796726256001307227] |