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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 9 |
| 4 | 56 |
| 5 | 190 |
| 6 | 1704 |
| 7 | 7644 |
| 8 | 93120 |
| 9 | 516240 |
| 10 | 8136000 |
| 11 | 53523360 |
| 12 | 1047548160 |
| 13 | 7961241600 |
| 14 | 187132377600 |
| 15 | 1611967392000 |
| 16 | 44311886438400 |
| 17 | 426483893606400 |
| 18 | 13428757601280000 |
| 19 | 142790947407360000 |
| 20 | 5066854992138240000 |
| 21 | 58981696577556480000 |
| 22 | 2328441680297779200000 |
[1,1,4,9,56,190,1704,7644,93120,516240,8136000, 53523360,1047548160,7961241600,187132377600, 1611967392000,44311886438400,426483893606400, 13428757601280000,142790947407360000, 5066854992138240000,58981696577556480000, 2328441680297779200000] |