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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 24 |
| 3 | 144 |
| 4 | 828 |
| 5 | 4624 |
| 6 | 25296 |
| 7 | 136192 |
| 8 | 723160 |
| 9 | 3792564 |
| 10 | 19672240 |
| 11 | 101054512 |
| 12 | 514643952 |
| 13 | 2600665872 |
| 14 | 13049557280 |
| 15 | 65057605120 |
| 16 | 322413671228 |
| 17 | 1589046496704 |
| 18 | 7791836790504 |
| 19 | 38025622117168 |
| 20 | 184749163375664 |
| 21 | 893881787650016 |
| 22 | 4308024769339344 |
| 23 | 20685919693884672 |
[1,4,24,144,828,4624,25296,136192,723160,3792564, 19672240,101054512,514643952,2600665872, 13049557280,65057605120,322413671228, 1589046496704,7791836790504,38025622117168, 184749163375664,893881787650016,4308024769339344, 20685919693884672] |