| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 4 |
| 3 | 60 |
| 4 | 556 |
| 5 | 5328 |
| 6 | 45316 |
| 7 | 405636 |
| 8 | 3583136 |
| 9 | 30801264 |
| 10 | 261702184 |
| 11 | 2204389124 |
| 12 | 18485952896 |
| 13 | 154072120428 |
| 14 | 1276431617512 |
| 15 | 10525735832272 |
| 16 | 86463238965520 |
| 17 | 707822586795020 |
| 18 | 5776135319900600 |
| 19 | 47001025464956044 |
| 20 | 381480686633266156 |
| 21 | 3089168335328298424 |
| 22 | 24963223479997963992 |
[0,0,4,60,556,5328,45316,405636,3583136,30801264, 261702184,2204389124,18485952896,154072120428, 1276431617512,10525735832272,86463238965520, 707822586795020,5776135319900600, 47001025464956044,381480686633266156, 3089168335328298424,24963223479997963992] |