| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 42 |
| 5 | 308 |
| 6 | 2424 |
| 7 | 21118 |
| 8 | 194010 |
| 9 | 1866896 |
| 10 | 18674908 |
| 11 | 192737280 |
| 12 | 2042585592 |
| 13 | 22142680360 |
| 14 | 244772420336 |
| 15 | 2752312897942 |
| 16 | 31415853441050 |
| 17 | 363394473652344 |
| 18 | 4253708877703476 |
| 19 | 50326069309616132 |
| 20 | 601181906802967564 |
| 21 | 7244698219481190376 |
| 22 | 88003741534163878912 |
| 23 | 1076851417694238454896 |
[1,0,2,6,42,308,2424,21118,194010,1866896, 18674908,192737280,2042585592,22142680360, 244772420336,2752312897942,31415853441050, 363394473652344,4253708877703476, 50326069309616132,601181906802967564, 7244698219481190376,88003741534163878912, 1076851417694238454896] |